Neutral lipid urine fractions of women and men were analyzed for the phosphomolybdic acid and cupric ion-reducing substances and for formaldehyde generating substances. Diurnal variations in output of these substances correlated positively. Benzene-water partitions seemed to offer no advantage since the ratio of reducing substances and formaldehyde-generating substances in the 2 fractions did not change significantly after diurnal stress of ACTH admn. Non-alcoholic reducing substances varied between 4% and 20% of total reducing substances and did not change in proportion after ACTH admn. For routine assay of corticoids in urine the phosphomolybdic acid reducing method of Heard and Sobel had the advantage of economy, rapidity and relatively low variability.