For a finite adsorption rate, generally the coupling of adsorption and condensation causes a time dependent supersaturation. This coupling can be described in an explicit way by the predator-prey model. The influence of the time dependent supersaturation on the progressive and instantaneous nucleation mechanism was investigated by numerical simulations for different parameter sets. The slope m, obtained for the Avrami plots serves as a diagnostic criterion for the nucleation and growth mechanism. The conventional concepts assuming a constant supersaturation yields integer values for the slope m, whereas the Avrami plot itself is linear. In contrast to this, the time dependent supersaturation causes a broad range of slopes m, whereby the Avrami plot itself deviates from linearity depending on the course of the concentration-time curve for non-condensed molecules. (C) 2002 Elsevier Science B.V. All rights reserved.