A black family with two male infants affected with the X-linked Lowe syndrome was studied. All three females in the pedigree were found to be carriers on the basis of lenticular opacities. Each female had one son. Of these, two were affected and one was unaffected. The Xg blood-group locus and the G6PD locus were determined in these six individuals. Two of the carrier females were heterozygous for G6PD isoenzymes A- and B. Skewing of the A-:B ratio in isolated erythrocytes, lymphocytes, granulocytes, platelets, and cultured skin fibroblasts from these females may be the result of either selection against cells expressing the Lowe gene product or random X-chromosome inactivation. At least one instance of recombination was found between the G6PD and the Lowe syndrome loci. At least two instances of recombination occurred between the Xg blood-group and Lowe syndrome loci.