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14C ring-labelled hydrocortisone, testosterone and benzoic acid dissolved in acetone were applied to the backs of guinea-pigs (4 microgram/cm2). Percutaneous absorption was quantified by following the excretion of tracer in urine and faeces for 5 days. Absorption of hydrocortisone and benzoic acid was 2.4% (s.d. = 0.5; n = 3) and 31.4% (s.d. = 9.1; n = 3) of the applied dose respectively, similar to published human absorption data. Testosterone was absorbed to a greater extent in guinea-pigs (34.9% +/- 5.4; n = 5) than man. A thioglycollate based depilatory cream significantly increased the skin absorption of testosterone, while the absorption velocity was unaltered. Two analytical methods were compared, direct counting versus wet ashing; results were in the same range for the three compounds. Two methods of quantifying skin absorption were compared; urine recovery corrected for incomplete urinary excretion after parenteral administration versus the addition of urine and faecal recovery. For benzoic acid, excreted mainly in the urine (88.1%), the two methods gave similar results; for testosterone, excreted in the urine to a lesser extent (46.8%), the method of addition of urine and faecal recovery appeared to be more correct.