Using the California Mastitis Test (CMT), 736 quarters corresponding to 184 animals from 3 farms with medium milk production in the province of Los Ríos, randomly chosen, were evaluated. From the positive quarters (reactions from traces to very positive cases) a milk sample was taken to perform the test (CMT). 52.17% were positive, according to the intensity of the reaction, 30.89% were very positive (+++), 75.97% were positive (++), 49.43% were slightly positive (+) and 13.87% traces. The risk factors were evaluated with the Guide of Good Livestock Milk Production Practices. Agrocality. 2012, chapters IX, X and XI with the respective literals. 55.88% was compliance with regulations, followed by 26.47 % and 17.64% of the farms evaluated. The estimated economic losses of US 8,174inthethreeherds,correspondingtoUS 96 per cow and US 0.31percow/day.Compliancewiththeregulationswouldreducetheincidenceofsubclinicalmastitisonfarmswithmediumandsmall−scaledairyproductionsystems.MediantelapruebadeCaliforniaMastitisTest(CMT),seevaluaron736cuartoscorrespondientesa184animalesde3fincasdemedianaproduccioˊndelecheenlaprovinciadeLosRıˊos,escogidasaleatoriamente.Deloscuartospositivos(reaccionesdesdetrazashastacasosmuypositivos)setomoˊunamuestradelechepararealizareltest(CMT).El52,17 8174 en los tres hatos, correspondiendo a US96porvacayaUS 0,31 por vaca/día. Con el cumplimiento de la normativa se reduciría la incidencia de mastitis subclínica en las fincas con sistemas de producción de mediano y pequeño nivel de producción láctea