Familial hypercholesterolaemia (FH) is an autosomal dominant disorder of lipid metabolism characterized by elevated low-density lipoproteins (LDL), the formation of tendon and skin xanthomata and the development of premature coronary atherosclerosis. It is caused by a defect in the receptor-mediated hepatic uptake of LDL due to mutations in the LDL receptor. In 25 FH families with a total of 160 members and in two individuals without available relatives, all of German origin, we identified LDL receptor mutations by a multiplex-PCR-based single-strand conformation polymorphism method followed by direct sequencing. Of the 24 mutations found, 15 are missense mutations, 2 are nonsense mutations, 4 are small deletions or insertions leading to frameshifts, 2 are an in-frame insertion and deletion, respectively, and one is a splice site mutation. Propositi carrying mutations that are known to completely abolish receptor function (nonsense and frameshift mutations, missense mutation V480M) had significantly higher untreated total and LDL-cholesterol levels compared to those patients carrying missense and in-frame insertion mutations of unknown functional consequence, which may lead to either reduced or completely abolished receptor function (11.30+/-1.64 vs 9.76+/-1.50 mmol/L, and 9.39+/-1.23 vs 7.99+/-1.45 mmol/L, respectively). These results confirm the clinical and molecular heterogeneity of FH and the influence of different functional classes of mutations on lipid values.