ABSTRACTField research was conducted in central England on grasses infected byEpichloëtyphina.Both asymptomatic and stromata-producing infections were encountered and examined. Isolations of endophytes were made and comparative laboratory studies conducted on sugar utilization capacities, starch and protein hydrolysis capacities, and cultural morphologies. The presence of distinct varieties ofAcremonium typhinumis proposed to account for variation in ecology, physiology, and morphology of isolates.