The public health and veterinary significance of sewage transmissible helminth infections is largely underestimated. Since land application is the ultimate destination of mu.ch of the sludge produced, this study was designed to investigate the longevity of helminth parasites in such material. The initial aim of the investigation was to develop reliable and quantitative isolation techniques. After determining specific gravity values for the ova of Taenia and Ascaris, several methods of isolating these were compared and modified to improve the efficiency of recovery. The effectiveness of sewage treatment for the removal of these ova was examined by measuring sedimentation rates. These values indicated that the retention times currently used in treatment plants must often be inadequate • .Anaerobic mesophilic digestion had no observable effect on the removal of ova. A number of criteria for judging the viability of ova were used to investigate the persistance of helminth ova stored in raw, digested and dried-cake sludge. Treated sludges were found to provide the leas:t favourable conditions for egg survival. The influence of ultraioletv light, temperature and humidity on egg survival was studied. Of these, humidity had the most detrimental effect. In situ lysimeter experiments were conducted to examine both persistance and viability of helminth ova under field conditions. Under the cirumstances tested Ascaris ova were found to persist longer than Taenia ova. Calves were infected. experimentally with ova recovered from raw sludge in order to obtain conclusive proof that such eggs were infective; ova retained infectivity upto 3 months. This work contributes to the understanding of the fate of animal parasites in sludges a:p:plied to agricultural land and may therefore be used to assist in the drafting of responsible policies for the safe use of sludge in agriculture.