Pediat. R e s . 10: 189-192 (1976 Extract after chickenpox infection. Two groups of normal children were studied as controls, one group before chickenpox infection and one Chromosomes were studied in 74-hr lymphocyte cultures from group during and I and 3 months after infection. ~h~ ages and seven patients with Down's syndrome and from 12 he ma to logic all^ sexes ofchildren included i n study are in ~~b l 1 and karyotypically normal control subjects. Six were studied be-and 2, fore and six after chickenpox infection. In Down's syndrome, the number of breaks per cell was 0. and also significantly greater than the number of breaks, 0.046 * trisomy 21 who ranged from 2--6 years of age and from six control 0.023, observed in control children with chickenpox. Therefore, children with normal karyotypes and normal hematologic findings, chromosomes from patients with Down's syndrome were signifi-2-6 years of age. Chickenpox was diagnosed clinically from the cantly more sensitive to breakage after chickenpox infection than appearance on the skin and mucous membranes of successive crops those from control subjects. of typical vesicles which was generally accompanied by a mild The incidence of chromosome breaks in Down's syndrome 1 constitutional reaction. Children with atypical chickenpox were month after chickenpox infection fell to the level observed in the excluded from this study. Blood samples were collected 1-3 days preinfection range. The present results showed that the difference after onset of the specific rash, and subsequently 1 and 3 months between the observed and the expected values for breakage in special after infection. N o individual had received either x-rays for regions of chromosome was not significant, but that chromosome diagnosis or chloramphenicol therapy in the recent past. breakage was random.) Chickenpox Down's s y n d r o m e c h r o m o s o m e d a m a g e