The influence of hormonal oral contraceptives on the urinary porphyrin excretion of 40 healthy females has been studied. Two different hormonal oral contraceptives (combinations of gestoden or desogestrel, respectively, and ethinylestradiol) were applied for half a year. In each case twenty women received one of these two combinations. Porphyrin precursors delta-aminolevulinic acid and porphobilinogen were normal in all subjects as well as the mean of uroporphyrin and coproporphyrin. One healthy female developed a mild secondary coproporphyrinuria. In this case coproporphyrin isomer I was slightly enhanced and isomer III slightly lowered. Furthermore it could be shown that three females with repeated premenstrual clinical expression of an acute hepatic porphyria (acute intermittent porphyria and hereditary coproporphyria) could be treated successfully with a hormonal oral contraceptive or other exogenous hormones to stabilize the latent, subclinical phase of the disease.