The female reproductive organs of Ascaris lumbricoides represented one fifth of the total fresh weight and contained two thirds of the total body lipids. These lipids consisted of saponifiables (79%) and unsaponifiables (21%). Phospholipids of the lecithin–cephalin type were present, as well as an abundance of triglycerides. The latter contained unusually large amounts of C2—C0 saturated volatile acids among which acetic and hexanoic acids predominated. Ascaryl alcohol was the major constituent of the large unsaponifiable fraction, and on the basis of previous chemical analyses and of infrared spectra a hypothetical structure is proposed. A sterol mixture containing significant proportions of both saturated and unsaturated components was also isolated, but not identified further.