We introduced continuous intravenous infusion of amphotericin-B (AMPH-B) to extremely low birthweight (ELBW) infants (< 1000 g) with or without renal failure as a single agent for treating definite or probable systemic candidiasis. The species of Candida isolated from blood or tracheal aspirate or urine were C. albicans in seven infants, C glabrata in two, C. tropicalis in one and C. parapsilosis in one. The minimal inhibitory concentrations (MIC) of AMPH-B required against these isolates were less than 0.2 micrograms/mL except for that against one strain of C. albicans (0.78 microgram/mL). Serum AMPH-B levels were 0.31-0.78 (0.51 +/- 0.14) micrograms/mL when doses of 0.2-0.55 (0.32 +/- 0.11) mg/kg per day were being administered. The serum level was higher than the MIC of each isolate in all but one infant who died of disseminated intravascular coagulation and Candida pneumonia. Another infant died of congenital heart disease. The other nine infants survived. The serum level showed no correlation with the daily dose. The ratio of the serum level to the daily dose (L/D ratio) showed a significant correlation to serum creatinine (r = 0.787) and the linear regression curve followed the equation: L/D ratio = 0.223 x serum creatinine + 1.11 (P < 0.01). Few adverse effects due to AMPH-B were noted. Our data may give a simple reference to serum AMPH-B levels during continuous intravenous infusion from the dose and the serum creatinine level.