The systemic absorption of amphotericin B, administered as a 10 mg lozenge, was investigated in 14 patients with malignancies, who received three or four doses daily during chronic administration. The mean plasma amphotericin B concentration, measured 3 h after the morning dose on from 1-20 occasions over a 1-80 day period, ranged among subjects from 46 +/- 13 ng/ml (s.d., n = 20) to 136 +/- 25 ng/ml (n = 19). Using the previously reported intravenous clearance of the drug, the fraction of the dose absorbed was estimated at 8.3-9.9%. This is considerably greater than that estimated from earlier reports (0.2-0.9%), which used much higher oral doses (2-10 g/day).