Levels of unconjugated testosterone, 5alpha-dihydrotestosterone, oestradiol and progesterone in human urine were measured before and after storage at various temperatures. Specific radioimmunoassays were used for all measurements. Levels did not change at -20 degrees C, and no change was detected at 4 degrees C for up to 5 days. Testosterone showed an average increase of 100% in 2-3 days at 18 degrees C and 5alpha-dihydrotestosterone about 200%. At 37 degrees C, the rise was two to three times faster still. The addition of enzyme inhibitors, bacteriostatic agents and various salts had no effect on the increase of the unconjugated androgens. Adjustment of the pH of samples to 2 caused about 4-fold rise of the androgens within 10 min, but at pH 8.6 there was no significant effect. Unconjugated oestradiol and progesterone levels showed a rise in a few samples at 18 degrees C for three days. At 37 degrees C both hormones showed a rise after 18 h in about two-thirds of samples, about 2-fold for progesterone and 6-fold for oestradiol.