1. Dissection of the parathyroid glands post mortem is greatly facilitated by the recognition of their opacity to transmitted light. The location of these glands before or at operation is being attempted by the use of radio -isotopes. On the principle that all radiation is harmful, it is suggested that the possibility of employing transillumination be investigated. It should be possible to illuminate them with an intra-oesophageal light source, either primary or secondary, suitably collimated and cooled. 2. A proper appreciation of their cytology requires thi sections; these may be attained by simple variation of standard methods. 3. A staining method has been evolved for the ready identification of the oxyphil cells. It is reasonably reliable on necropsy material, even if somewhat demanding technically. Its evolution was guided by histochemical theory and in practice it fulfils the criteria of maximum tinctorial density and considerable selectivity on thin sections. Its colour also lies in the region of the spectrum to which the eye is most sensitive, a highly desirable feature in a stain to' be used for the study of cytological granules for prolonged periods. 4. The previously reported great variation in the total weights of the glands is confirmed; there is also a great variation in area as between the glands of an individual. 5. On the evidence of the overlap of v ghts and numbers of glands, it is suggested that on occasion one may accept fewer than the conventional 3 or 14 glands as the normal number. On a number of occasions two glands will be as large as a set of four nearby. 6. Adipose tissue may be present or absent in any decade. 7. Glands devoid of fat are commoner in the first decade than subsequently. 8. The commonest level of adipose tissue in a gland is below 10%. Assuming that anything above this should be regarded as a fatty gland, such cases were reviewed regarding their nutritional status as recorded on the necropsy report. There is only a slight correlation with bodily obesity, almost half being from the normally nourished. A number were from the emaciated. 9. The distribution of fatty glands within Table is not systematic enough to be able to say more from it than that large glands tend to contain more fat. A diposity does not equate with atrophy under normal c ircumtances. 10. The average gland contains relatively little fat but individuals may show great variation between their glands. The assessment of atrophy on the evidence of such estimations must be difficult in the extreme. 11. The greatest amounts of fat lie in the 50 - 70% range and may occur at any point along the table of:mean parenchyma volumes. 12. Oxyphil cells are probably always present. 13. The oxyphil cell counts show, tentatively, the same type of distribution as has been reported by others, i.e up to a normal level of some 8% in the female and 5% in the male in the 9th. decade. 14. These figures are rather lower perhaps because of my separate treatment of the oxyphil cell islets. These rarely amount to more than a few percent of the parench area and although large areas do tend to occur against the background of a high oxyphil cell count this is by no means invariable. 15. Inspection of the post mortem diagnoses of those showing either high counts, islets or both was quite unrewarding. My own material tended to associate them with senile dementia or intracranial aneurysms while from general hospital practice the association was more with atherosclerosis, hypertension and myocardial infarction; these "associations" are purely a reflection of the types of work done in different hospitals. The suggested correlation of oxyphil cell population with the latter group of conditions is, I believe, spurious; it would certainly require a very rigorous investigation to confirm its validity. 16. No general correlation between oxyphil counts and obesity can be demonstrated. 17. No light is cast upon the problem of the oxyphils by this study. An insignificant fraction of a tiny organ we know nothing of the total amount of "oncocytes" present in an individual's other organs; it may be that these cells form a system of unknown function. 18. Enlightenment may perhaps come from repetition of the work demonstrating their hyperplasia following the administration of thiourea.