Two populations of normal persons were investigated for associations of acrocentric chromosomes in lymphocyte cultures. We studied in the first series (macrocultures), 1,300 metaphase cells from five males and eight females, in the second series (microcultures), 1,550 metaphase cells from 31 males and 31 females. In the second series all the absolute values were significantly lower than in the first series. In both populations no statistically significant sex differences were observed. Differentiating between D-D, D-G and G-G associations, a relative increase of G-G associations could be shown. In a double variance analysis, performed with the results of the first series, a high stability of individual association patterns could be shown. In a single χztest of the second series significant deviations from the expected D-D, D-G and G-G associations for the individuals were observed.