Various isolates ofTrichodermaspp. formed chlamydospores in oat kernels placed in sterile and natural soils and in excised tissues of corn and bean inoculated with a conidial suspension. In an axenic oat – loam soil system, isolates of three species (T.viride,T.harzianum,T.hamatum) produced 1–38 × 107chlamydospores/g of oat tissue. The soil type and its organic matter content did not affect the number of chlamydospores formed. In oat kernels retrieved from natural soils infested withTrichodermaconidia, approximately 10% were chlamydospores of indigenousTrichodermaspp. that infested and colonized the oats. Another 10% were attributed to the isolates added to soils as conidia. The remaining chlamydospores belonged toFusariumspp., unidentified fungi, or were nongerminable on the media used. In excised corn and bean tissues infested withTrichoderma, from 19 × 106to 61 × 106chlamydospores/g of tissue were formed by the phyllosphere fungi. Ten percent of the chlamydospores were from the introduced isolates and the remainder from indigenousTrichodermaspp.,Fusariumspp., and unidentified fungi. The results suggest the probable importance ofTrichodermachlamydospores in the survival of this genus in soil.