Four pregnancies at risk for mucopolysaccharidosis VII were monitored by chorionic villus sampling obtained in the first or second trimester of gestation. One fetus showed reduced beta-glucuronidase activity following simultaneous sampling of chorionic villus and amniotic fluid at 17 weeks of gestation. The pregnancy was terminated. Subsequent assay of beta-glucuronidase activity in the fetal tissues was consistent with a diagnosis of mucopolysaccharidosis VII, thus confirming that chorionic villus samples provide useful information for diagnosis of this condition.