The magnetic behaviour at T = 0 K of a system consisting of conduction electrons coupled to localized electrons submitted to an axial crystal field is studied in the molecular field approximation. We assume that the exchange parameter J varies spatially, with a Gaussian probability distribution. We define an average ionic magnetic moment and obtain the condition for spontaneous magnetic order, involving the crystal field parameter, the width and the mean value of the exchange parameter distribution. We also obtain graphs of the magnetic moment versus mean value of the exchange parameter distribution, for different distributions showing that the distribution of J`s reduces the rate of increase of magnetization versus the mean J. (author).