In a prospective randomized study, contamination rates of disposable pressure transducers changed every two days (n = 81) were compared with those changed at four (n = 26) or eight days (n = 50); the mean daily incidence of contamination was 3% for each group. After four days of use, the cumulative prevalences of contamination were similar. However, after eight days, the cumulative prevalence was significantly higher in transducers used without change (6.9%) than in those changed every two days (2.9%). Gram-negative bacilli were present in 63% of contaminated transducers; over half were from the patients' own flora. The only definite transducer-related bacteremia occurred on a day of initial contamination and should have been unaffected by the interval of change. Routine use of disposable transducers can be safely extended to four days, even in a busy intensive care unit.