Infection of primary human embryo kidney cells with adenovirus types 2, 7, 12, 18 and 31, at a multiplicity of infection of 2, resulted in the induction of chromosome aberrations in metaphases examined 24 hr after infection. The aberrations induced by types 2 and 7 were randomly distributed over the karyotype, but types 12 and 31, and to a lesser extent type 18, all induced non-random effects. Both type 12 and type 31 produced chromatid and isochromatid gaps and breaks at a specific site on chromosome no. 17.