Nematode parasitism of cotton (Gossypium hirsutum L.) has become increasingly important because of yield losses and increased distribution across cotton production regions. Penetration and reproduction of root-knot nematodes, Meloidogyne incognita (Kofoid & White) Chitwood, Race 3, was compared on three cotton genotypes differing in level of resistance: M-8, susceptible to root-knot; M-78 (M-78RNR), moderately resistant; and M-315 (M-315RNR), resistant. Responses were characterized by penetration of plant roots by root-knot nematode juveniles and by reproduction, measured as number of eggs, egg-masses per plant, and eggs per egg-mass. Susceptible, moderately resistant, and highly resistant cotton genotypes were penetrated about equally by juveniles. Production of egg-masses, eggs per egg-mass, and eggs per plant by nematodes were different among the three cotton genotypes. The development of egg masses was delayed in M-78 and M-315 as compared with M-8, with the greatest delay and prevention of the formation of significant numbers of egg-masses in the highly resistant M-315. Production of eggs and second-stage infective juveniles in the moderately resistant M-78 were sufficient to contribute significantly to the build-up of the next generation of root-knot populations in cotton production fields. Reproduction on M-315 was so low that nematode populations would be expected to decrease significantly under continuous culture. M-315 possesses two major genes for resistance and is a valuable source of root-knot nematode resistance for cotton improvement programs. These genes in combination do not alter penetration of the root-knot nematode juvenile stage into cotton roots, but do have major negative effects on survival and reproduction of the nematodes.