Sister-chromatid exchange (SCE) and rates of proliferation in human amniotic fluid cells from healthy donors exposed to human IFN-alpha and IFN-beta and recombinant IFN-alpha and -beta were investigated. Amniotic fluid cells were obtained from pregnant women undergoing genetic amniocentesis. For 46 h, cells were treated with IFNs at concentrations of 10(3)-10(5) U/l. A dose-depending decrease of SCE rate with IFN-alpha and IFN-beta was observed. Our studies in amniotic fluid cells show that the mean SCE frequencies are reduced after incubation with IFN-alpha as well as with IFN-alpha. In contrast to IFN-gamma, the type I IFNs IFN-alpha and IFN-beta cause a genetic effect on DNA repair or a protection from DNA damage. Previously we had shown that a significant dose-depending increase of SCE rates was found in amniotic fluid cultures after addition of IFN-gamma. Therefore, IFN-alpha and IFN-beta (both human IFNs) and also recombinant IFN-alpha and IFN-beta, also in high doses, are neither genotoxic/clastogenic nor embryotoxic. Amniotic cells are vulnerable human cells, which may be well suited for examining the effects of agents like interferon.