Verticillium wilt, caused by Verticillium dahliae Kleb., is a major constraint to cotton production in almost all countries where cotton is cultivated. Developing new cotton cultivars resistant to Verticillium wilt is the most effective and feasible way to combat the problem. Little is known about the inheritance of resistance to Verticillium wilt of cotton, especially that caused by the defoliating (D) and nondefoliating (ND) pathotypes of the soil-borne fungus V. dahliae. The objective of this study was to determine the inheritance of resistance in cotton against both pathotypes of V. dahliae. Crosses were made between the susceptible parent 'Cukurova 1518' and each of four resistant parents PAUM 401, PAUM 403, PAUM 405 and PAUM 406 to produce F-2 generations in 2002 and F-2:3 families in 2003. Disease responses of parent and progeny populations to the D and ND pathotypes were scored based on a scale of 0-4 (0, resistant; 4, susceptible). F-2 populations inoculated with the D pathotype showed a 3 : 1 (resistant : susceptible) plant segregation ratio. Tests of F-2:3 families confirmed that resistance was controlled by a single dominant gene. In contrast, analysis of data from F-2- and F-2-derived F-3 families suggested that resistance to the ND pathotype is controlled by dominant alleles at two loci.