The effects of methionine on fragmentation and vacuolation in Acremonium chrysogenum was examined during growth on different carbon sources. Cells exhibited a filamentous form during exponential growth phase, which was followed by a yeast-like morphology in the stationary stage. Cultures also underwent a vacuolation process, monitored by the average cell diameter. The first phenomenon was correlated with growth, the latter seemed to be related to the sugar consumption rate. Methionine addition increased growth rate by accelerating sugar consumption, enhanced the vacuolation process, and increased the specific cephalosporin-C production rate.