Pseudomonas cepacia or Enterobacter species or both were isolated from blood cultures of 79 patients in a community hospital between April 1971 and March 1972. No common exposures other than venipuncture correlated with positive blood cultures. Pseudomonas cepacia, Enterobacter, and other Gram-negative enteric bacteria were cultured from aqueous benzalkonium chloride used for skin antisepsis prior to ordinary and blood culture venipuncture. Contamination of blood cultures by organisms from the antiseptic most likely accounted for positive cultures in 35 to 38 patients (92%) with P cepacia. The remaining three patients had repeated blood cultures positive for P cepacia and circumstantial clinical evidence of bacteremia; they may have contracted disease through exposure to the contaminated antiseptic. Substitution of an iodine-alcohol antiseptic abruptly reduced the isolation of P cepacia and Enterobacter.