A total of 775 pure-strain and F1 mice were obtained from a 6 X 6 diallel mating plan. Previous factor analysis of 42 measures of emotionality identified 14 behavioral factors, ten of which were interpretable. Hayman's analysis of variance and analysis of diallel crosses were applied to each of the factors. In general, the findings indicate that the mode of inheritance for emotionality factors is polygenic and in the direction of complete dominance. However, a major point of this investigation is that the mode of inheritance of highly complex behavior such as emotionality depends on the factor in question. For example, the breakdown of dominance effects by factor was as follows: partial dominance--Motor Discharge, Food Motivation, Tunneling-2, and Activity Level (males); complete dominance--Audiogenic Reactivity, Underwater Swimming (males), and Activity Level (females); overdominance--Acrophobia, Territorial Marking (males). Additional findings include directional dominance for Underwater Swimming and Audiogenic Reactivity, and significant sex differences for eight of the 14 factors.