Experiments were conducted to determine genetic variability, heritabilities, and genetic correlations of yield components, resistance to Phytopthora infestans, Alternaria solani, and Meloidogyne in eight F2 and five F3 tomato (Lycopersicon esculentum) populations. Three methods were utilized to calculate heritability: (1) Parent-Offspring Regression, (2) Variation among F3 Families, and (3) Components of variance. In the F2 and evaluation for late bliqht (P. infestans) indicated that all eight populations were susceptible to this disease. In the F3 populations were moderately resistant to susceptible to the rootknot nematode (Meloidogyne) but there was no statistical differences among families. The populations were also quite susceptible to A. solari. The amount of genetic variation for yield components varied depending on the population and trait. Although heritabilities varied according to method of calculation, in general, total and commercial yields had low heritabilities across all populations. Number of fruits was often associated with intermediate heritabilities and weight per fruit with intermediate to high heritabilities. The two variance component methods gave similar results while the parent-offspring regression technique resulted in low and non-significant heritabilities. Commercial yield was significantly and positively correlated with most of its components and negatively correlated with nodule number, per cent defoliation, and rate of defoliation. In view of the low heritabilities Single Seed Descent is suggested as a useful breeding technique for selection of the traits discussed.