An egg-production function was constructed, using data collected from 366 commercial layer flocks in California, to predict the impact of Mycoplasma gallisepticum (MG) and M. synoviae (MS) on egg production while controlling for confounding factors. In the first and second cycles, respectively, an MG-infected flock produced 12 and 5 fewer eggs per hen than an uninfected flock. Flocks that became infected with MG after F-strain vaccination produced 6 eggs/hen more than unvaccinated infected flocks in the first cycle, but no significant difference was observed between such groups in the second cycle. No association was found between MS-infection and egg production. Commercial layer producers in Southern California lost an estimated 127 million eggs because of MG in 1984. This lost egg production and associated MG-control-program costs amounted to an estimated financial loss of approximately $7 million. This represented a loss of approximately $6 million in consumer surplus.