Following our recent suggestion that antiferromagnetism of UPt3 can be understood within the crystal field splitting scheme and that the observed below 5 K AF correlations are dominated by thermal fluctuations, we examine here the effect of a uniform magnetic field on these correlations. Orientations of field in the basal plane and perpendicular to it are considered. The field of a few teslas must have a pronounced effect which can be used as a check of the suggested scheme.