Abecarnil is a beta-carboline derivative that occurs in three modifications, A, B and C, and shows a special type of polymorphism. Two thermodynamically unstable but closely related modifications with nearly the same solubility and a stable polymorph are known. The polymorph nucleated is in most cases one of the two unstable forms, its type is determined by the type of solvent and crystallization kinetics, While not entirely dry, the modifications readily undergo a solution mediated phase transformation, which is, in the case of the two unstable forms, of the contact model type. The kinetics of the transformation is drastically reduced in the presence of trace amounts of an acid. It is shown by microcalorimetry and sampling of mother liquor, that the system extremely rapidly reaches the saturation curve, i.e. Abecarnil crystallizes very easily, Due to this phenomenon, Abecarnil can be crystallized by spray drying and a novel form of direct contact cooling with the same solvent, The modification obtained in these cases is always the most unstable B form, which is attributed to the extremely high supersaturations during nucleation.