A novel synthetic cyclopeptamine, A172013, rapidly accumulated by passive diffusion into Candida albicans CCH442. Drug influx could not be totally facilitated by the membrane-bound target, -(1,3)-glucan synthase, since accumulation was unsaturable at drug concentrations up to 10 µg/ml (about 1.6 × 10⁷ molecules/cell), or 25× MIC. About 55 and 23% of the cell-incorporated drug was associated with the cell wall and protoplasts, respectively. Isolated microsomes contained 95% of the protoplast-associated drug, which was fully active against glucan synthesis in vitro. Drug (0.1 µg/ml) accumulation was rapid and complete after 5 min in several fungi tested, including a lipopeptide/cyclopeptamine-resistant strain of C. albicans (LP3-1). The compound penetrated to comparable levels in both yeast and hyphal forms of C. albicans, and accumulation in Aspergillus niger was 20% that in C. albicans. These data indicated that drug-cell interactions were driven by the amphiphilic nature of the compound and that the cell wall served as a major drug reservoir.