The aim of the present study was to evaluate the following parameters of silage maize ear length: variability of inbred lines and their diallel hybrids, superior-parent heterosis and general and special combining abilities. According to obtained results of the two-year study, it can be concluded that variability of this trait is significantly affected by a genotype and a genotype x year interaction. As expected, hybrids had greater average values of ear length than inbreeds due to the depression of this trait that occurs in inbreeds during inbreeding. The highest average value of heterosis for ear length was detected in the hybrid ZPLB 402 x ZPLB 406 (62.3% and 48.8% in 1997 and 1998, respectively). The estimation of combining abilities was done on the basis of diallel hybrids after the method established by Griffing, 1956a (method II, mathematical model I). The analysis of variance of combining ability for ear length indicated highly significant positive values of GCA and SCA for the observed trait in both years of investigation. Ear length inheritance was more affected by non-additive genes (dominance and epistasis) as indicated by the GCA to SCA ratio that was smaller than unity. The inbreeds ZPLB 401 and ZPLB 406 had high GCA effects, while the hybrid combinations ZPLB 401 x ZPLB 403. ZPLB 401 x ZPLB 402, ZPLB 401 x ZPLB 406 and ZPLB 403 x ZPLB 406 had high SCA effects in both investigation years. These hybrid combinations include both parents with high GCA effects or one parent with low GCA effects. Furthermore, there are combinations ZPLB 403 x ZPLB 405 and ZPLB 404 x ZPLB 405 with significant SCA effects that include parents with low GCA effects. This is probably a result of the additive type (additive x additive) of interaction between parents.