The transmission of strongyles among 54 Shetland-cross mature ponies was examined from May 30 to November 22, 1983 when the ponies were on pasture and over the ensuing winter when they were in loose housing. Fecal and pasture herbage samples were taken fortnightly through the pasture season and periodically thereafter. Three foals born and reared on pasture were weaned and removed from pasture, two in early August and one in mid-September, and housed for a period before necropsy. Daily maximum and minimum air temperature and total precipitation were recorded. The mean fecal strongyle egg count was highest in the spring and early summer and lowest over the winter. Few larvae were found on the herbage in late May and their numbers were near zero by the third week in June. Subsequently, the numbers increased, were highest from late August through to mid-October and then declined and were low over the winter. Few strongyles were found in two foals removed earlier in the season, and many in the one later. The transmission of strongyles appeared to occur, therefore, principally from mid-summer to mid-fall.