The safety of amphotericin B colloidal dispersion (ABCD) was tested in five open-label Phase I/II clinical trials in 572 selected patients who had a fungal infection secondary to a severe underlying disease. In 442 cases ABCD was administered after therapy with amphotericin B, which had been withdrawn in 192 of them because of toxicity. One hundred and forty patients had pre-existing nephrotoxicity. ABCD doses of up to 6 mg/kg/day resulted in no differences in serum creatinine levels, even in patients with pre-existing renal failure. ABCD therapy resulted in no difference in liver function as measured by SGOT, alkaline phosphatase and total bilirubin levels in serum. Apart from thrombocytopenia, there was no significant alteration in hematological or other biochemical parameters in the blood. Adverse events attributable to ABCD requiring discontinuation of therapy occurred in 70 patients (12.2%). The most frequent of these were infusion-related adverse events, which occurred in 5.4% of patients. As a consequence, the maximum tolerated dose was set at 7.5 mg/kg/day. These studies show clearly that ABCD can be administered safely to patients without the risk of renal toxicity, even when renal impairment has already developed following therapy with conventional amphotericin B deoxycholate.