The gynaecological tissue levels of miocamycin were studied in ten female patients after pre-operative administration. The patients were divided into two groups on the basis of the scheduled sampling time. All the patients received 4200 mg of the drug, divided in 7 tablets of 600 mg each every 8 h, last administration 2 or 3 h before surgery. The tissue levels, obtained by means of the microbiological method (Sarcina lutea 9341), were frequently higher than those obtained in the serum at the same time. Miocamycin reached the highest concentration in the endometrium (2.5 micrograms/g) and the lowest in the vagina (1.1-0.8 micrograms/g).