Growth of 3 reference bovine C. fetus strains in media with and without antibiotics and bacteriostats active against the most common contaminant bacteria in the bovine genital tract was evaluated. In addition, 2 regional bovine C. fetus strains and 1 reference C. sputorum biovar bubulus strain were used in some experiments. Reference strain C. fetus subsp. venerealis was completely inhibited by polymyxin (> or = 0.25 IU/ml) whereas the other C. fetus strains were not inhibited. In Shepler's medium supplemented with rifampicin (10 micrograms/ml) subsp. fetus, was the only one to grow. When rifampicin was used at 5 micrograms/ml together with a reduced dose of the other Shepler's antibiotics, especially polymyxin B (0.85 IU/ml), subsp. venerealis was able to grow; nevertheless even at such a reduced dose, rifampicin was inhibitory for the biotype intermedius. It was demonstrated that triclosan (Irgasan) could be very useful at < or = 10 micrograms/ml in media with added blood, < or = 6 micrograms/ml in brucella broth and < or = 3 micrograms/ml in Mueller-Hinton broth for isolation of all subspecies of C. fetus. The sensitivity of C. fetus to 5-fluorouracil was variable: subsp. fetus was resistant (up to 800 micrograms/ml) whereas subspp. venerealis and biotype intermedius grew slowly or sometimes did not grow at all in concentrations of 6.25 micrograms/ml onwards. Fosfomycin was inhibitory to all C. fetus strains at > or = 50 micrograms/ml. C. sputorum biovar. bubulus was less inhibited than C. fetus with triclosan grew up to more than 100 micrograms/ml, with 5-fluorouracil up to 100 micrograms/ml and with fosfomycin up to 50 micrograms/ml. Growth of C. fetus subspp. was compared in different microaerophilic atmospheres contained in anaerobic jars (Oxoid HP 11) without palladium catalyzer. Growth with nitrogen or hydrogen was similar. When jars were replaced by 15 x 13 cm cylindrical cans without valves or gas measurement devices only pure hydrogen supported satisfactory growth of all C. fetus subspp. and C. sputorum biovar. bubulus strains. The candle system, a commercial nitrogen rich gas mixture and pure carbonic anhydride prepared in these cans failed to enable these strains to grow. C. fetus subsp. fetus was more aero-tolerant than subsp. venerealis and its biotype intermedius and was able to grow, although very weakly, with only carbonic anhydride added to an aerobic atmosphere. The growth obtained using a commercial gas generating microaerophilic kit (Oxoid BR-56) was comparable to the one achieved with the hydrogen rich atmosphere prepared in our laboratory.