In recent years, in the Federal Republic of Germany an increase in the prevalence of Coxiella burnetii infections in cattle has been well documented and its association with infertility problems in this species has been postulated by a number of authors. Investigations on this problem have been hampered by the fact that another intracellular agent, Chlamydia psittaci, which may also cause infertility, is also highly prevalent in the cattle population. Vaccination trials with a commercial egg-propagated inactivated vaccine against both agents have indicated that fertility in infected flocks may be improved significantly by application of such a vaccine. However, since this combined vaccine occasionally induces severe local reactions in vaccinated animals, it still needs further improvement. Limited experiments with more purified experimental C. burnetii vaccines have shown that Q fever in cattle may be prevented by vaccination of young uninfected animals only. In this way herds free of C. burnetii may be established.