Four cotton varieties belonging to Gossypium barbadense L Le.Giza80, Giza83, Australian and Pima early were selected as parents and crossed In a half diallel pattern to evaluate general and specific combining ability effects (GCA and SCA) and heterosis effects for some agronomic traits i.e. boll weight (8W), seed cotton yield (SCY), lint yield (LY), lint percentage (L%), seed index (SI), lint index (U), micronaire value (Mic), pressly Index (PI) and Upper half means (U.H.M). Analysis of variance revealed significant differences among entries for all traits studied except for BW, Mic and PI in the F15 and BW and SI in Fis which showed insignificant differences. The mean squares, in both F_t's and Fis for general combining ability (GCA) were significant for all traits except for BW In F_I's, SI and U.H.M in F2's and Mic values in both populations (F₂ and F2). Meanwhile the mean squares for specific combining ability (SCA) were significant for LY, L%, SI, U and U.H.M in F_t's and SCY, LY, L% and Mic values In F₂'s. The GCA/SCA ratio of variance components Indicated that additive genetic variance was generally of greater importance for SCY, LY, L%, SI and P1 in the F_n hybrids and for 8W, SCY, LY, SI, U, PI and U.H.M in the F2 generation. Mid-parents heterosis values were significant and positive for U.H.M cross Giza83 x Pima early (P2 x P4), SCY, LY and U.H.M cross Australian x Pima early (P3 x P4). On the other hand significant negative heterotic values were observed for BW cross Giza80 x Australian (P1 x P3), BW, L%, U, PI and U.H.M ass Giza80 x Pima early (P1 x P4), BW, SCY, LY, SI, U, PI and U.H.M cross Giza83 x Australian (P2 x P3), LY, L% and U cross Giza83 x Pima early (P2 x P4) and BW, SI and PI cross Australian x Pima early (P3 x P4). Only slight heterosis values relative to the better•parent were observed in this set of material for all characters studied except for SCY in cross Giza80 x Australian (P1 x P3) and BW cross (Australian x Pima early (P3 x P4) that gave significant positive estimates to the heterotic effects relative to better-parent. Regarding inbreeding depression, significant negative effects were obtained for Mic values cross Giza80 x Australian (P1 x P3), U, Mic and U.H.M cross Giza8b x Pima early x P4) and cross Giza83 x Pima early (P2 x P4).