The aim of the study was to investigate factors influencing survival and growth of Pinus sylvestris L. at a natural tree-line. Five experimental stations were set up along an altitudinal transect from 290 m to 675 m at Creag Fhiaclach in the Cairngorm Mountains, Scotland. Three further stations were established in the University grounds at Edinburgh, two of which were inside greenhouses. Thus, a climatological gradient was obtained. Eight 2 year-old Pinus sylvestris of Scottish provenance were potted into pea/sand compost and placed at each of the eight stations and measurements of height extension, needle length and fascicle number were made during 1989 and 1990. Similar measurements were also made on five native trees at each station along the transect. Air and meristem temperatures were measured and monthly means calculated for all stations. Mean monthly air and meristem temperatures decreased with increasing altitude. Growth of P.sylvestris was found to vary with altitude and can be accounted for at least in part by temperature variation. Height extension, fascicle number, percentage needle survival and needle length decreased with increasing altitude, mean height extension and mean number of fascicles being positively correlated with mean meristem temperatures of the previous (May to June) growth season. Cuticles of needles from all trees measured along the transect were isolated by acid digestion (5% chromic acid) and no significant difference was found in cuticular weight per surface area between altitudes. Results are discussed in relation to the hypothesis of Tranquillini (1979) on the causal relationships leading to winter desiccation of shoots at alpine tree-lines. The hypothesis is considered inappropriate to Scots pine in Scotland. Needle water potential varied with altitude only in the potted trees related to their age and susceptibility to fluctuating conditions. Needle nutrient concentrations varied significantly with time, needle age and altitude, being higher in valley trees than above the tree-line. Low values were thought to be related to poor nutrient availability, restricted root growth and the effects of low temperatures. Photosynthetic rates of native P.sylvestris were higher in valley trees than in those above the tree-line early in the season due to a developmental lag caused by temperature. By September, rates were higher above the tree-line and plants showed an adaptation of increased quantum efficiency. Percentage needle loss over winter was similar between valley and above tree-line populations, possibly through the effect of frost acting at the lower station. The relevance of the present study is discussed in relation to other tree-lines and to future predictions of tree growth with respect to climatic warming. Suggestions for further work are proposed.