Surveillance of hospital-acquired infections and antibiotic use is required of US hospitals. The time and cost needed to actively perform this surveillance can be extensive. We developed a computerized infectious disease monitor that automatically generates four types of surveillance "alerts" for patients (1) with hospital-acquired infections, (2) not receiving antibiotics to which their pathogens are susceptible, (3) who could be receiving less expensive antibiotics, or (4) who are receiving prophylactic antibiotics too long. Surveillance personnel using computer screening for two months found more hospital-acquired infections when compared with our traditional surveillance methods, while requiring only 35% of the time. In addition, alerts from the computer identified 37 patients not receiving appropriate antibiotics, 31 patients who could have been receiving less expensive antibiotics, and 142 patients, during one month, receiving prolonged cephalosporin prophylaxis. Computer screening can help focus the activities and improve the efficiency of hospital surveillance personnel.