We performed antifungal susceptibility tests with cilofungin (LY121019), amphotericin B, and flucytosine against 38 strains of yeasts from patients with esophagitis or fungemia either before, during, or after treatment with cilofungin. Tests were performed using a macrobroth dilution method similar to that proposed by the National Committee for Clinical Laboratory Standards (M27-P) and two microbroth methods. For cilofungin and amphotericin B, minimum inhibitory concentrations from microbroth tests using Antibiotic Medium 3 (AM3) were systematically lower than results from the other two methods that utilized RPMI-1640 medium (RPMI). AM3 did not provide any greater degree of in vitro correlation with clinical results than did RPMI. We conclude that cilofungin and possibly other congeners of the echinocandin class of antifungal agents can effectively be studied using the proposed National Committee for Clinical Laboratory Standards method. © 1994.