We investigated the relevance of prominent reduction in turbidity macroscopically (MIC) and formation of aberrant hyphal tips microscopically (minimum effective concentration; MEC) in measuring the in vitro activity of caspofungin against Aspergillus and Fusarium. Caspofungin generated low MICs and MECs against Aspergillus, but not for Fusarium. While MICs increased inconsistently when the incubation time was prolonged, MEC appeared as a stable and potentially relevant endpoint in testing in vitro caspofungin activity.