Cystic fibrosis (CF) is a common autosomal recessive disorder among people of European origin. With the localisation of the gene locus to chromosome 7q31 and the identification of closely linked polymorphic markers in 1985, it became possible to offer prenatal testing to couples at risk of having CF children, provided a live affected individual from that family was available for investigation. The CF gene, named CFTR, was cloned and sequenced in 1989 and the most common CF-causing mutation, delta F508, identified. A search for this mutation has been carried out in 81 South African white CF families of European origin. Using the polymerase chain reaction (PCR) technique the frequency of delta F508 was found to be 0.81. This mutation was not found in the 1 negroid and the 1 Indian CF family investigated.