The distribution of sister chromatid exchange (SCE) points has been analyzed in cultured lymphocytes from three age-groups of 30 females (n = 10; young: 13-20, middle-aged: 30-55, old: 75-84 years). The observed interchromosomal SCE distribution is in good agreement with the results of previous workers, significant age-dependent differences could not be established. It has only to be mentioned that chromosome E16 showed a relative SCE deficiency in young females, a result which has to be affirmed by further studies. Analysis of intrachromosomal SCE distribution revealed a surplus in the midarm section of most chromatid arms. Besides very similar distribution patterns in all three age-groups, there were some, mostly insignificant differences which had to be verified by further investigation.