We report on a patient with a de novo chromosome abnormality del(7)(q21.1q22). The cells of this patient were used to determine the assignment of the gene for the enzyme beta-glucuronidase and the DNA probes around the cystic fibrosis gene--pJ3.11 and metH. Both the beta-glucuronidase gene and the DNA probes pJ3.11 and metH were found in 2 copies in our patient, indicating that neither locus lies in the deleted segment.