Using a quantitative sonication method, we cultured 1,681 consecutive vascular catheters submitted to a clinical microbiology laboratory in a 36-month period. A total of 46% of the cultures were positive; the most common organisms isolated were coagulase-negative staphylococci (36.4%), Pseudomonas aeruginosa (13.9%), enterococci (10.0%), yeasts (9.2%), Staphylococcus aureus (5.8%), and Enterobacter species (4.4%). The frequencies of positive blood cultures within 48 h prior to a positive catheter culture result were as follows: Candida albicans (68.4%), S. aureus (60%), Enterobacter cloacae (42.9%), Staphylococcus epidermidis (32.1%), P. aeruginosa (27.7%), and enterococci (23.3%). The sonication method allowed quantification of the number of CFU removed from a catheter for between 10(2) and 10(7) CFU. For catheter cultures in which greater than or equal to 10(2) CFU grew, a linear regression equation could be calculated: (risk of positive blood culture for the same organism) = 14 [log10 (number of organisms removed from the catheter)] -21 (r = 0.93). For catheter cultures in which less than 10(2) CFU grew, positive blood cultures for the same organism were strongly associated with a proven infection at a site distant from the catheter (P = 0.001) or probable contamination (S. epidermidis). Our findings indicate that this technique has considerable potential for use in clinical microbiology laboratories to aid in the diagnosis of vascular catheter infections and for clinical investigations into the pathogenesis of these infections.