Estimation of general (GCA) and specific (SCA) combining abilities of lines, gene effects as well as extraction of the best hybrid combinations for plant height and head diameter is integral part of sunflower breeding program at the Agricultural Institute Osijek. It conducts it due to choice of lines that will enable creation of hybrids with good agronomic traits. The research included 6 inbred lines, 15 single crosses, 15 experimental three way and three approved hybrids. Only F1 direct

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... were used in the estimation of combining abilities. Significance of differences among mean values of hybrids was tested by LSD test, in the first year in relation to mean of trial, and in the second year in relation to commercial hybrid Orion being a standard hybrid for approval of new sunflower hybrids. On both localities, the highest GCA effects for plant height were realized by the line L-5, and for head diameter line L-103. The lowest SCA effects for plant height had crosses 5A x 103B and 101A x 302B. The best combinations for head diameter are 5A x 302B and 103A x 219B. Portion of genetic in relation to environmental variance was higher for plant height, and lower for head diameter. The research has shown that additive gene effects for plant height were more important than dominant effects, but for head diameter dominant effects were more important.