During the 10-year period 1950-1960 the incidence of Trichomonas gallinae among several series of mourning doves shot or trapped in Maryland has varied from zero to 12 1/2 percent. Prior to 1959, all isolations of T. gallinae from doves during such surveys had been from birds with well-developed lesions. In 1959, trichomonads were demonstrated in three of 54 normal hunter-killed doves examined in Howard County. The incidence of trichomonad infection among doves which were submitted to the laboratory because they were obviously diseased was much higher. Of 44 clinically ill doves submitted during the period 1950-1960,25 were found to be infected with T. gallinae. In the Maryland area the incidence of trichomonad infection among mourning doves appears to be low, but when infection does occur it is usually due to a pathogenic strain which produces a typical fatal canker.