Effective measures for protection of laboratory staff against infections due to experiments with pathogens are a challenge for safeguarding against hazards. Investigations on limited epidemic infections and their causes are of high relevance. During an experiment with pregnant sheep 5 of 7 persons who took part in the operation procedures developed Q fever 10 to 24 days after exposure. One sheep aborted spontaneously 3 days after the third experiment. Examinations of the aborted material revealed Coxiella burnetii, Chlamydophila psittaci, and Staphylococcus chromogenes. Coxiella burnetii and Chlamydophila psittaci were also detected in some of the other placentae. This outbreak of Q fever during an experiment with infected sheep affected more than 70% of the people involved with this experiment and shows the high risk of working with the zoonotic agent Coxiella burnetii. Hence, technical, organizational, and personnel measures have to be taken, and laboratory animals are to be monitored to prevent further infections.