Organic solid solution pigments are prepared and conditioned by treating a mixture of their components, after synthesis but preferably without or with only partial drying, in a mixture of from 0 to 30% by weight of an organic liquid having a dipole moment of 2.8-6.010^-18 .esu (2.8 to 6.0 debye units) and from 70 to 100% by weight of water in an agitated media pearl mill having a specific power density of at most 2.0 kjs^-1 per liter of grinding space. Drying the starting components is especially suitable in the case of only slightly agglomerating, easy to wet pigments of specific surface area from 1 to 25 m²/g. The method gives excellent results, and is flexible and also much simpler than known methods.