Accumulation of autophagic vacuoles (AVs) is a phenomenon observed in various cells treated with the microtubule inhibitor vinblastine. In order to test whether the accumulation of AVs is a result of retarded fusion of autophagosomes and lysosomes an investigation was carried out to ascertain whether other antimicrotubular drugs, e.g., nocodazole and griseofulvin, also induce accumulation of AVs. Ehrlich ascites tumor cells were incubated with nocodazole (20 micrograms/ml) or griseofulvin (50 micrograms/ml). Morphometric analyses were performed after incubation periods of 3, 30, 60, and 120 min. The volume densities of autophagic vacuoles did not differ significantly from the control values after the various incubation periods tested. It was concluded that intact microtubules are not needed in the fusion of autophagosomes and lysosomes and that vinblastine accelerates the rate of AV formation.