Plants obtained from seed of 16 Spanish and 6 German provenances of Scots pine (Pinus sylvestris L.) were installed at five trial sites distributed throughout the natural range of the species in Spain. Five years after planting (7 years of age) the experimental material was measured for total height, diameter, number of twigs at the fourth year whorl and survival. The analysis confirmed that the rate of height growth of the Spanish is lower than that of the German provenances, whereas for the other traits the best Spanish compare favourably with the Germans. Provenance by site interaction was very significant (P < 0.01) for most traits. Attempts to model the interaction of Spanish provenances on height by simultaneous introduction of some climatic and geographic covariates on both factors were not successful but a multiplicative model with one bilinear term was enough to provide a sensible explanation of this interaction. Usually, provenances closest to each trial site were found better adapted than more distant ones but some provenances of close origin presented a different behaviour. Processes of adaptation and selection of these ancient populations could be considered as the main factors to cause this interaction.