Among 116 patients with biopsy-confirmed chronic hepatitis C (Riba 2 or Riba 3 positive) in a multicenter study in southern Norway on interferon, we determined hepatitis C virus genotype by restriction fragment length polymorphism (RFLP) of the 5' NCR. The RFLP method was supplemented by and compared with a serological typing method based on the detection of type-specific antibody to peptide from the NS-4 region. A total of 102/106 (96%) patient sera showed detectable type-specific antibody to NS-4 peptides and corresponded in all cases, except two, to the genotype detected by polymerase chain reaction. Combining the results from RFLP genotyping and serotyping, genotype 1 was found in 40 (35%) (27 with 1a and 10 with 1b, 3 subtypes not determined), genotype 2 in 15 (13%) (subtype 2b in 14 and 1 subtype not determined), and genotype 3 in 58 (50%) of patients. The low mean age of the patients (34 years), the low prevalence of cirrhosis (3.5%), the short duration of the disease, and a high prevalence of intravenous-drug abusers may account for the low prevalence of infection with genotype 1b (9%). The epidemiological features of hepatitis C patients are markedly different from patient groups described in southern Europe in terms of risk factors, age, and genotype distribution.