Trichoderma virens is an effective biocontrol agent of soil-borne pathogens that affect the cotton root system such as Rhizoctonia solani and Fusarium oxysporum. However, its ability to induce systemic protection in cotton is unknown. Other Trichoderma species are reported to induce systemic resistance in other crops, e.g. T. harzianum in bean and T. viride in tobacco and grape. Therefore, T. virens might also provide some systemic protection. Cotton seeds (cvs. DeltaPine 50 and Rowden) were treated with dried preparations of Trichoderma virens in a wheat bran and peat moss carrier or with carrier alone as a control, and planted in field soil. The T. virens strains used are highly effective for controlling damping-off in cotton seedlings. Two strains of T. virens, a "P" strain, effective against Pythium ultimum, and a "Q" strain, effective against Rhizoctonia solani, were included in the tests. When cotton plants had six true leaves, the plants were inoculated with Verticillium dahliae by stem puncture. After 10 days, plant heights were measured and plants were examined for foliar symptoms to determine Verticillium wilt severity. Plants treated with the "P" strain of T. virens, strain G4, were significantly taller than untreated control plants. This suggests a possible growth promotion activity with this strain. Treatment with either of the two strains of T. virens reduced the disease severity rating significantly in Verticillium dahliae-inoculated plants on both cultivars (a=0.05). This suggests that T. virens may induce a systemic resistance response in cotton. However, no increased stimulation of terpenoid phytoalexins or tannins was observed in the stems of cotton plants with the T. virens treatments. Therefore this resistance response does not appear to be due to priming of the plant to respond more rapidly to pathogen attack.