A microbiological assay was undertaken to measure the amounts of clofoctol in human plasma and pulmonary tissue, and to investigate its pharmacokinetics. Clofoctol was extracted from samples using ethanol and the concentration of drug in the extracts was determined by the broth macrodilution method using as reference microorganisms S. aureus ATCC 29213 and B. cereus NCIB 8122, whose MIC values were 0.537 and 1.074 micrograms/ml respectively. This procedure allows the almost complete recovery of the drug and makes it possible to detect amounts of clofoctol as low as 5.5 micrograms/ml. Results indicate that clofoctol is well absorbed after a single rectal dose of 1.5 g, with a plasma Cmax at the 30th min after administration and an average AUC value of 80.91 micrograms/ml/h. The Cmax of lung tissue (which was higher than the plasmatic one) occurred at the 90th min and the average AUC value was 229.65 micrograms/ml/h, indicating good penetration of clofoctol into human lung tissue and appreciable tissue storage of the drug.