The effect of the medium composition on the fungistatic (MIC) and fungicidal (MLC) activity of amphotericin B, itraconazole, voriconazole, posaconazole and terbinafine against four Aspergillus fumigatus strains has been investigated by four European laboratories. MICs were determined by broth microdilution, using RPMI 1640 and Antibiotic Medium 3 (AM3), three times in three independent determinations by the four laboratories. MLCs were determined for the three independent determinations by the four laboratories, subculturing 100 microl from each well showing no visible growth after 48 hours. Except for a 2-dilution difference observed in three cases, no differences were observed between MICs determined on the two media. In contrast, a 3- to 6-dilution discrepancy between the MLCs was observed for the azoles. Endpoints on RPMI were higher than those on AM3. A 1-2 dilution difference was noted between both the endpoints of amphotericin B and of terbinafine. The highest inter- and intra-laboratory agreements were reached on AM3. The azoles showed a medium-dependent fungicidal activity.