In a prospective surveillance study (February 1990-December 1991) performed at a 1000-bed teaching hospital to identify risk factors for nosocomial methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, 309 patients were found to be colonized (n = 103; 33%) or infected (n = 206; 67%) by MRSA. Sixty-three of them developed bacteremia. Compared with 114 patients who had nosocomial bacteremia caused by methicillin-sensitive Staphylococcus aureus during the same period of time, MRSA bacteremic patients had more severe underlying diseases (p < 0.01), were more often in intensive care units (p < 0.01) and had received prior antibiotic therapy more frequently (p < 0.01). To further identify risk factors for MRSA bacteremia, univariate and multivariate analyses of this series of 309 patients were performed using the occurrence of MRSA bacteremia as the dependent variable. Among 14 variables analyzed, intravascular catheterization, defined as one or more intravascular catheters in place for more than 48 h, was the only variable selected by a logistic regression model as an independent risk factor (OR = 2.7, CI = 1.1-6.6). The results of this study reinforce the concept that recent antibiotic therapy may predispose patients to MRSA infection and suggest that among patients colonized or infected by MRSA, those with intravascular catheters are at high risk of developing MRSA bacteremia.