Diffusion of miokamycin into gum, maxillary-mandibular bone and crevicular fluid was studied in human beings. The antibiotic concentrations were determined in specimens at different times after oral administration of 600 mg in a single dose of miokamycin. Peak serum levels (2.32 +/- 0.67 mcg/ml) were found at the first hour after dosage. In healthy gum tissue the highest antibiotic levels (1.44 +/- 0.34 mcg/gr) were observed at the second hour, while in the inflamed gum miokamycin penetrates more rapidly, being, as in serum at the highest levels detectable during the first hour. In the bone of the maxilla or mandible the highest levels of miokamycin (0.88 +/- 0.13 mcg/gr) were detected at the second hour after treatment. In the crevicular fluid miokamycin showed a similar profile as that in serum, since the peak levels were reached at the first hour (2.4 +/- 0.88 mcg/ml, but the decrease of the antibiotic occurred more slowly than in serum. Miokamycin rapidly penetrates into tissues and fluids of oral cavity. A single oral dose of 600 mg guarantees antibacterial levels against susceptible bacteria over six hours.