Recently, increased spontaneous chromosome instability was reported in couples with recurrent spontaneous abortions but without constitutional chromosome aberrations. Therefore, we investigated the frequency and distribution of aphidicolin-induced common fragile sites in couples with recurrent spontaneous abortions and no children and in age-related control couples. The breakage rate was significantly elevated in the abortion-prone couples; the women in the abortion couples had an especially higher breakage rate than the control women. Breakpoints cluster to those chromosome regions where common fragile sites have been localized. No preference of a particular common fragile site was demonstrated in the abortion couples. Our findings appear to support the hypothesis of increased chromosome instability in at least some couples with recurrent spontaneous abortions. As long as the nature of aphidicolin-induced common fragile sites is not completely understood, the significance of these findings remains unclear.