Ungerminated ascospores of Dipodascopsis uninucleata contained 18 times more lipid (5.5 % dry wt) than germinated cells; the lipid comprised 58 % (w/w) glycolipids, 28 % (w/w) neutral lipids (mainly triacylglycerols)and 14 % (w/w) phospholipids (mainly phosphatidylcholine and phosphatidylethanolamine). During germination the absolute amounts of all three lipid fractions fell sharply but, during the subsequent initiation of hyphal growth,the amount of phospholipids increased. As these hyphae began to differentiate for the sexual stage of the life cycle,the amount of neutral lipid then increased. The fatty acyl groups of the glyco-, neutral and phospholipid fractions throughout the life cycle were mainly palmitate (16:0), oleate (18: 1) and linoleate (18:2). The percentage of 16:O remained constant during the life cycle while the relative amounts of 18:2 plus alpha-linolenate (18:3) in the glyco-,neutral and phospholipid fractions first increased during initiation of growth and then decreased during the onset of differentiation. The opposite trend occurred with 18: 1. When [(3)H]arachidonic acid (ARA) and [1-(14)C]181: were fed separately to D. uninucleata, both were rapidly incorporated into phospholipids. Highest incorporation of ARA was in the growth phase; during the onset and remainder of the differentiation phase, the amount of ARA decreased in this fraction. Incorporation of 18: 1 increased during growth and differentiation, with a significant proportion(49% to 57%) being incorporated into triacylglycerols compared to a much smaller proportion (12% to 17%) of ARA.