Psoriasis vulgaris is a multifactorial disease; the strongest association was established with the HLA complex. The actual disease-predisposing gene(s) has not been identified yet, but several genes from this region were examined in addition to HLA-C and -B. However, HLA-linked complement component polymorphic genes were not extensively studied. Therefore, we typed 67 psoriatic patients for alleles of the HLA-linked complement components BF, C4A and C4B. Alleles of C3, encoded on another chromosome, were established in parallel as a negative control. Frequencies in patients were compared with those in unrelated healthy controls, 100 individuals for C4A and C4B, 890 for BF and 4719 for C3 We found no association of BF alleles with disease, similarly to C3. Among C4 alleles, C4B*3 was present in 13.4% of patients as compared with 1% of controls (OR, 15.36; 95% CI, 1.897-124.42; P=0.0009), and C4A*6 was present in 19.4% of patients versus 7% of controls (OR, 3.20; 95% CI, 1.202-8.508; P=0.0155). The high frequency of C4B*3 in psoriatics has not been described so far. These results suggest a contribution of C4 genes themselves or a closely linked gene to the susceptibility to psoriasis.