Human adenoviruses 1 to 28 were shown to produce a cytopathic effect in Vero cell cultures. Viruses of subgroups III and IV (Ad 1, 2, 5, 6, 12, and 18) were readily passaged in Vero cell cultures and were produced in high amounts. This was also found for Ad 11, 16, and 21, while Ad 3, 4, and 7 showed a lower degree of multiplication and Ad 14 could not be passed serially. For Ad 8, 26, 27, 20, 25, and 28, a multiplication in Vero cells could not be proved, while the remaining serotypes of subgroup II showed a moderate degree of multiplication. The sensitivity of Vero cells to small amounts of virus was lower than that of HeLa cells. No adaption of adenoviruses to Vero cells after 5 Vero passages was observed. Attempts to enhance virus multiplication by coinfection with SV40 failed.