We compared the diagnostic value of quantitative cultures of bronchoalveolar lavage (BAL) and telescoping plugged catheter (TPC) samples in 34 nonimmunocompromised, mechanically ventilated (MV) patients with suspected bacterial pneumonia. A control group of seven "noninfected" MV patients was also studied. In 92% of patients with bacterial pneumonia (32 of 34), simple endotracheal aspiration samples recovered one or more microorganisms. Both BAL and TPC samples cultured colony-forming units (cfu) greater than or equal to 10(3)/ml of one or more microorganisms in 56% (19 of 34) of patients. TPC and BAL culture results agreed on 88.5% (54 of 61) of the recovered microorganisms. Sterile TPC and BAL cultures agreed on 80% (4 of 5) of the cases. Microorganisms cultured from blood samples were also cultured from BAL and TPC specimens. Culture results from the two techniques completely disagreed in only one case (3%). In the control group, one TPC and two BAL cultures yielded microorganisms in cfu greater than or equal to 10(3)/ml. Specificities of BAL and TPC were 71 and 86%, respectively, whereas specificity of endotracheal aspiration was only 14%. Both the bacterial index obtained by TPC and BAL, as well as the quantitative cultures, correlated moderately well (r = 0.78 and 0.72, respectively, p less than 0.001 for both correlations). BAL and TPC results caused changes of antibiotic treatment in 11 of 23 survivors. Neither BAL nor TPC caused complications. Our results demonstrate that BAL and TPC diagnose bacterial pneumonia in MV patients with similar accuracy. Culture results from both techniques showed excellent qualitative and reasonable quantitative agreement.