This paper presents results of the computation of models for main-sequence stars having homogeneous chemical composition, in the phase of hydrogen reactions. Fourteen mode1s having convective core and radiative envelope are considered, with masses 4, 5, 8, 10 and 16 $M\odot$ and chemical structure $0.650 \leqslant X \leqslant 0.900$, $0.01 \leqslant Z \leqslant 0.045$. These models are compared with models of other authors and with observational results. The computed chemical composition of stars from the upper part of the zero main sequence is: X = 0.650, Z = 0.40. The M - L relation for two different chemical structures is presented. The influence of the variation in chemical composition on the Kramers opacity law and the interpolation formula based on the Keller and Meyerott tables is discussed.