Chronic C hepatitis is a global health problem. Its treatment is still unresolved. Pegylated interferon means substantive breakthrough in therapy. The longer effect, the lasting, steady therapeutic blood level are the pharmacokinetic advances. There is no significant difference in the side effects of pegylated interferon and standard interferon. The most frequent side effects leading to dose reduction or cessation of the treatment are depression and hematologic disorders. Neutropenia is induced more frequently by pegylated interferon, than by the standard form according to the literature. Combined antiviral treatment (pegylated interferon alpha-2a and ribavirin) of a 54 years old woman, who suffered from posttransfusion chronic hepatitis C was started. The dose of the pegylated interferon alpha-2a and ribavirin was reduced at the 8th week due to leucopenia and mild anemia. Fever, cough, sore throat and weakness occurred. Agranulocytosis was detected which was accounted as a side effect of pegylated interferon treatment. Antibiotic, antimycotic therapy and filgastrim was given. Leukocyte number increased, fever stopped after 10 days of therapy. The patient returned 17 days later. She had been having high fever, weakness, sore throat for 4 days. Ciprofloxacin was given by GP before her registration because of the suspicion of urinary infection, then she took sulfamethoxazol + trimethoprim without medical advise. Agranulocytosis was detected again, Staphylococcus sepsis developed. No sign of hematologic disease was found in the bone marrow. Agranulocytosis was considered aftermath of sulfamethoxazol + trimethoprim. Antibiotics, antimycotic and antiviral treatment, and filgastrim were given, sepsis healed, leukocyte number became normal. 274 patients suffering from chronic hepatitis C were treated by standard interferon, and 43 were treated by pegylated interferon. Rapid and significant decrease of leukocyte count was observed in the patients treated by pegylated interferon in the first 4 weeks of the treatment then it remained stable. Cessation of the treatment or dose-reduction was not necessary due to neutropenia among patients treated by standard interferon, while dose reduction was reasonable in two more cases in addition to this one, treated by pegylated interferon. The authors stress the importance of the exact follow-up of patients according to the protocol, which renders the early recognition of side effects, the prevention of complications, and their early and adequate treatment possible. Thus, pegylated interferon--inspite of its marked side effects and more serious suppressive effect on bone marrow--is the most effective drug for the treatment of chronic hepatitis C.