We analysed the LDL receptor (LDLr) gene in 18 Brazilian patients with familial hypercholesterolaemia (FH) from 10 unrelated families. The combination of a direct search for the Lebanese allele of the LDLr gene by a PCR method and Southern blotting using cDNA probes allowed the identification of the gene defect in six out of 10 families. The Lebanese allele was found in five families and in one family the disease was caused by a 4 kb deletion in the 3' half of the LDLr gene. The results indicate an important contribution of the Lebanese allele to the prevalence of FH in the Brazilian population and suggest that it may also be the most common cause of FH in other mixed populations outside the Middle East.