Systemic fungal infection occurs in 2 to 4.5% of very low birth-weight (VLBW) infants (< 1,500 g) and may be fatal in 25 to 54%. Candida sp. is the major pathogen and amphotericin B the treatment of choice. To reduce side effects and optimize drug action, a formulation of amphotericin B encapsulated in liposomes (AmBisome) has been introduced. Data on 21 VLBW infants who received a full course of AmBisome was collected and its toxic effects with emphasis on nephrotoxicity and hypokalemia assessed. The median gestational age was 25 weeks (range 23-31) with a median birth-weight of 730 g (range 450-1,370). Antifungal therapy was started at a median age of 13 days (range 1-49). The median dose given was 2.6 mg/kg/day (range 1-5), and the median duration of therapy was 28 days (range 11-79), corresponding to a median cumulative dose of 71 mg/kg (range 12-271). Hypokalemia (< 3.0 mmol/l) was observed in 30% before, and 15% during AmBisome treatment. Twenty-one days after the termination of therapy, hypokalemia was not present in any patient. Median maximum daily potassium supplementation did not exceed doses usually recommended for VLBW infants. The median of the maximum creatinine levels before treatment was 121 mumol/l (range 71-221) and fell to 68 mumol/l (range 31-171) during treatment and 46 mumol/l (range 26-62) 21 days after the termination of therapy. All patients treated with AmBisome eradicated fungi and recovered clinically. AmBisome showed no certain nephrotoxicity in VLBW infants in this study.