The objetive of this study was to select. increase and apply sorne isolates of Trichoderma, and to evaluate their antagonistic activity against Sclerotinia sclerotiorum in vitro and in the field in chrysanthemum and snap beans. It was also intended to evaluate the efficiency of some fungicides in the control of those diseases. The isolates T10 of Trichoderma viride and T12 of Trichoderma harzianum were selected as the best antagonists for the greatest inhibition of mycelial growth. influence in the sclerotia production and sporulation of the pathogen. The isolates with a better antagonistic capacity were evaluated in the field. Significant diffarences were observed in the antagonistic effect between the isolates of Trichoderma. In field experiments the part of the plant most frequently affected was the upper part so that the application of fungicides should be targeted mainly to that plant part. The etficiency of application of. the fugicides ferbam, carbendazim and vizclozolin was also observed. The best control in the chrysanthemum trials was observed with a soil application of carbendazim during the first week after planting followed by five weekly applications to the foliage after the sixth week. When the best chemical treatment was comparad with the best antagonists differences between the two types of treatment were not observed.