1- This investigation was c~l'l'ip.tl out to study the general and specific: combining ability and heterosis of some characters ulling the cytoplasmic male-stel"ile phenomenon in some crosses of grain sorghum. z,- General combining ability (g. c. a.) and specific combining ability (s. c. a.) , variances were not significant fol" all characters studied. the g. c. a. effects wer e rnor e than the s, c. a. effects for plant height, 50% flowering. 1000 kernel weight and ear length. 3- The g. c. a. effects for female parents showed that only Mavttn A is
the best combiner for shorter plant height and earliness.
4- The g. c. a, effects for male parents showed that Giza IS was the best combiner for all cha r acte es studied except 50% flowering and ear width. Local z'9/6z' was the best combiner for 1000 kernel weight and ear length. Giza 114 had high general combining ability for grain yield/plant, head size and short plant height. Giza 54 proved to be a good combiner for plant height, plant grain yield and 1000 kernel weight.
5- All of the hybrids showing highly s, c. a. effects had a poor g. c. a. with their parents except Giza IS. 6- The g. c. a. variances were due to the additive effects of genes, while
the s, c. a. variances were due to the non-additive gene action. 7- Highly significant effects for heterosis were observed in plant height in all crosses studied from mid-parents, moreover the remaining characters showed highly significant effects for heterosis, in earliness, ear
length compared with better-parents. At the same tIme head size and 501. flowerIng showed negatlve heterotic effects from both mId-parents and better-parents.