Risk factors for cytomegalovirus and severe bacterial infections were studied prospectively by univariate, multivariate and time-dependent Cox model analysis in 79 consecutive liver transplant patients treated with selective bowel decontamination. Cytomegalovirus infection occurred in 39 patients (49%) and was symptomatic in 22 patients. Twenty-six patients (33%) developed at least one of 43 documented severe bacterial infections. In a multivariate analysis of risk factors for all cytomegalovirus infections, the cytomegalovirus seronegative recipient-cytomegalovirus seropositive donor group was the highest risk group (P < 0.001). Using the same analysis for risk factors for symptomatic cytomegalovirus infections, a prolonged prothrombin time (P < 0.005), a diagnosis of acute fulminant hepatitis as the underlying liver disease (P < 0.01) and a cytomegalovirus seronegative patient receiving a liver from a seropositive donor (P < 0.001) were significant. The treatment with OKT3 therapy (P < 0.008) and hepatic artery thrombosis (P < 0.02) were found to be significant risk factors in a time-dependent univariate analysis but were not independent risk factors when multivariate analysis was utilized. Significant risk factors for major bacterial infections (P < 0.03) using univariate analysis included a prolonged anesthesia, anhepatic and surgical times, as well as the transfusion of large amounts of fresh frozen plasma or autologous blood. In a multivariate analysis, only the transfusion of large amounts of fresh frozen plasma (P < 0.04) was a significant independent risk factor. Cytomegalovirus infection was a risk factor for the development of severe bacterial infections (P < 0.03) in a multivariate time-dependent analysis.