In a New Zealand Maori sibship of 9 (one a half-sib), 4 definite cases and 1 possible case of acute leukemia occurred in a space of 5 years. The children, 2 of whom were fraternal twins, developed symptoms at ages between 10 months and 6 years. One child had a marrow picture suspicious of leukemia nearly 2 years before the onset of symptoms.

Cytogenetic studies showed no major chromosome changes in either the parents or the 3 affected siblings examined. No linkage was found between the leukemias and any blood or serum group.

The nature of the factors causing the disease in this family is discussed.

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