This work aims to identify the mechanisms and kinetics of salicylic acid precipitation. A large supersaturation domain is covered (initial supersaturation ratios between 2.7 and 65.0) and two experimental set-ups are used. At low supersaturations, precipitations are performed in a stirred vessel, whereas a T-mixer must be used at high supersaturations in order to avoid hydrodynamic effects. In each case, the precipitation mechanisms actually involved are different and their kinetics are identified by solving the population balance with the method of classes. Thus, at low supersaturations in the stirred vessel, the primary nucleation is of heterogeneous type and the secondary nucleation is dominant, whereas homogeneous primary nucleation dominates in the T-mixer at high supersaturations. The crystal growth is diffusion controlled in the stirred vessel and turns into an integration limited mechanism in the T-mixer. (C) 2001 Elsevier Science B.V. All rights reserved.