A comparison of three different commercial media was made to assess their recovery of anaerobic organisms from the blood stream. The three media used were the 50-ml brain heart infusion broth with added CO2 (Pfizer), the 50-ml Thiol broth with added CO2 (Difco), and the 50-ml prereduced, supplemented peptone broth in a Vacutainer tube with added CO2 (Becton-Dickinson). During a period of 17 consecutive months, 12,216 specimens of blood were processed with each broth. Aerobic or anaerobic bacteria were recovered from 913 specimens (7%). Seventy-four specimens (8%) of the total positive cultures contained anaerobic organisms. When potential contaminants were removed from the totals, 7% of the positive cultures contained anaerobic organisms and 7% of the patients with positive cultures had bacteremia with anaerobic bacteria. Of the three commercial blood culture media studied, the prereduced, supplemented peptone broth recovered more anaerobic organisms than did either the brain heart infusion or Thiol broths.