The genotypes of 149 HCV strains from St. Petersburg were determined by limited sequencing and phylogenetic analysis within the NS5B region. One hundred two strains derived from patients that attended infectious disease clinics, of whom 48 admitted injecting drug use, and 47 derived from dialysis patients. Subtype 3a was predominant in the patients from infectious disease clinics, both in patients that admitted injecting drug use (56%) and in those with unknown source of infection (46%). However, 89% of the strains from dialysis patients belonged to subtype 1b. Eleven of twelve characterised strains from recent cases of hepatitis C at these units were at phylogenetic analysis shown to be related to strains already circulating there, demonstrating that within the dialysis units nosocomial transmission is the most important route of HCV infection. The predominance of subtype 1b strains in dialysis patients indicates that these strains have been circulating for a long time in dialysis units. The predominance of subtype 3a also among patients who did not admit drug use and that their strains were intermixed with the strains from injecting drug users in the phylogenetic analysis shows that the increase in injecting drug use is the major factor that explains the recent spread of HCV in the St. Petersburg population. This supports the concept that injecting drug use remains the major route for HCV infection in developed countries and that the control of drug abuse is the most important measure to prevent its spread.