Seeds of cowpea, Vigna unguiculata (L.) Walp, line ‘TVu 2027’ are moderately resistant to the cowpea weevil, Callosobruchus maculatus (F.). C. maculatus larvae exhibit higher mortality and take longer to develop in ‘TVu 2027’ than in more susceptible seeds. Claims have been made (Gatehouse, A.M.R., J. A. Gatehouse, P. Dobie, A. M. Kilminster & D. Boulter. 1979. Biochemical basis of insect resistance in Vigna unguiculata. J. Sci. Food Agric. 30: 948–958) that an elevated level of cowpea trypsin inhibitor (CPTI) confers resistance to ‘TVu 2027’. To test this hypothesis, we isolated and purified CPTI and evaluated its impact on cowpea weevil using an artificial seed system. CPTI at dietary levels up to 2.0% (wt/wt) caused no significant increase in mortality of cowpea weevils and only slight delays in within-seed developmental times. These results do not support the hypothesis that CPTI is the basis of resistance in ‘TVu 2027’.