"Se colectaron muestras de material vetegativo y suelo en varios sitios en el Estado de Zacatecas, durante el otoño de 1987 para estudiar la interacción de Fusarium-Rhizobium Rhizoctonia en el cultivo del frijol (Phaseolus vulgaris L.) Los organismos aislados fueron Fusariium sp., Rhizobium sp., y Rhizoctonia sp. Con la finalidad de establecer el efecto de los fungicidas captan y tiahendazol sobre el crecimiento de los microorganismos aislados, se efectuaron pruebas - in vitro. Encontrándose, que captan a una dosis de 1250 ppm v 1000 ppm inhiben respectivamente el crecimiento de Fusarium sp. y Rhizoctonia sp. Mientras, que el tiahendazol a una dosis de 5 ppm inhibió a los dos hongos de habito radical, para el caso de Rhizobium sp., el tiahendazol a 50 ppm estimuló el desarrollo bacteriano y lo contrario se observó en presencia de captan a 500 ppm.""Samples of vegetative material and soil were collected at several sites in the State of Zacatecas, during the tory of 1987 to study the interaction of Fusarium-Rhizobium Rhizoctonia in bean crops (Phaseolus vulgaris L.) The isolated organisms were Fusariium sp., Rhizobium sp., and Rhizoctonia sp. In order to establish the effect of the fungicides captan and thiahendazole on the growth of isolated microorganisms, in vitro tests were carried out. Finding that they capture at a dose of 1250 ppm and 1000 ppm respectively inhibit the growth of Fusarium sp. and Rhizoctonia sp. While thiahendazole at a dose of 5 ppm inhibited the two root-habiting fungi, in the case of Rhizobium sp., thiahendazole at 50 ppm stimulated bacterial development and the opposite was observed in the presence of captan at 500 ppm."