AbstractNearly all ascarosides in the ovaries ofA. lumbricoides occurred as esters. Among 15 identified esters, 13 occurred at concentrations exceeding 0.1% of the total ascarosides. Each ester consisted of one or two moles of glycone (ascarylose) and several homologs of long chain aglycone. The acid residues consisted of 95.6 mol % acetate and 4.4 mol % propionate. When present, propionate occurred only at the 2′ position of the glycone, which was always esterified. Esters with more than one free hydroxyl group were scarce, 89 wt % of the ascarosides being completely esterified. Monol aglycones contained 25–32 carbon atoms. The C29 homolog was most abundant, and ca. 25 wt% of these aglycones were branched and even‐numbered. Diol aglycones were unbranched C29–35 homologs, C31 and C33 being about equally abundant in diol ascarosides and C33 most common in diol diascarosides. Within each ascaroside class the proportions of different homologs were correlated with the extent of esterification. Free ascarosides of the ascaroside layer of the egg shell, which are formed from the ovarian esters, consisted of 12% monol ascaroside, 10% diol ascaroside, 8% diol diascaroside and 70% diol ascaroside containing an acetylated aglycone. The absence from ascaroside esters of the α‐methyl butyrate and α‐methyl valerate residues which are plentiful in ovarian triglycerides and waxes suggests considerable biosynthetic specificity.