The densities of states for LaCo 5 - x Ni x substitutional compounds were computed using the Haydock recursion method in a self-consistent procedure. The local magnetic moments were calculated for Co sites for which the Stoner criterion for ferromagnetism was found to be fulfilled. The decrease in magnetic moments with increasing Ni concentration is explained by the changes induced in the density of states by the added Ni atoms and the decrease in exchange splitting. The transition temperatures were computed in the framework of the spin fluctuation theory, the Stoner parameter decreasing with an increase in Ni concentration.