The chromosomes of two phenotypically normal individuals of a family with a complex chromosome rearrangement were studied. Karyotype analysis and measurements of certain chromosomes showed three abnormal chromosomes, and the apparently balanced karyotypes were interpreted as the result of reciprocal translocations between a B-, a C- and a D-group chromosome. The B- and D-group chromosomes involved were identified as a No. 5 and a No. 13 by means of autoradiography and the C-group chromosome as a No. 9 on morphological grounds.