Coccidioidomycosis is a mycosis firstly pulmonar caused by Coccidioides immitis; it can be disseminated to central nervous system, bones and skin, principaly. In Mexico, the real frequency of the disease is unknown. The aim of this work was to determine, by skin test and by serology, the infection cases by C. immitis in twelve communities (10 rural and two urban), attended in the Hospital Rural No 79 at the Instituto Mexicano del Seguro Social (IMSS) from the Coahuila State, Mexico. Six hundred and sixty eight adult individuals of both sexes were studied, to whom 0.1 ml of coccidioidin by intradermal route was applied; 72 h after, the induration diameter was measured. One hundred eighty individuals were selected and seric anti-C. immitis immunoglobulins levels were determined by ELISA. Six hundred twenty one individuals (93%) were positive to coccidioidin, the frequency was much higher than that previously reported in Coahuila. From 180 sera studied, the means of optical density (OD) were: IgG1, 1.55; IgG2, 0.94; total IgG, 0.33; IgG3, 0.29; IgG4, 0.27; IgM, 0.08. The values of IgG1, IgG2 and IgM compared with the other immunoglobulins were statistically significant. The high values of IgG1 and IgG2 suggest frequent contact with the antigen, and probable cases of undiagnosed disease.