AIMS--To determine the best medium for the primary isolation of Helicobacter pylori. METHODS--Sixty six gastric mucosal biopsy specimens frozen in 1 ml Cysteine Albimi media with 20% glycerol from 22 histologically proven H pylori infected patients were cultured on brain heart infusion agar (BHIA) with 7% fresh whole defibrinated horse blood, egg yolk agar (EYA), Columbia blood agar-cyclodextrin agar (CBA-Cd), and commercial trypticase soy agar (TSA) supplemented with 5% sheep blood. RESULTS--Successful primary isolation of H pylori was 96% with BHIA, 78% with TSA, 64% for EYA, and 32% with CBA-Cd. Colonies appeared earlier on BHIA (4.7 +/- 0.1 days, 5.3 +/- 0.4 days, 5.3 +/- 0.4 days, and 7.1 +/- 0.9 days for BHIA, TSA, EYA, and CBA-Cd) and there were more colonies on BHIA than on CBA-Cd, EYA or TSA (599 +/- 88, 104 +/- 66, 260 +/- 107, and 358 +/- 89, respectively). CONCLUSIONS--Success of a medium for passage of isolates apparently does not reliably predict usefulness for primary isolation. Freshly made BHIA with 7% horse blood medium is recommended for primary isolation. However, the easily obtainable TSA media would be the best alternative for routine clinical laboratories with no access to BHIA.