Net photosynthesis was measured in plants of four coffee varieties (two of Coffea arabica and two of Coffea canephoro (robusta) ) at several temperature and light conditions. It was observed that light saturation occurred at approximately 0.11 cal cm * min -1, whereas net photosynthesis decreased with increasing temperatures above 20 °C (approximately 7 % per °C). The arabica selection S288-23 showed the highest net photosynthesis and the lowest percentual decrease with excessive temperatures. The results are in good agreement with field experiments of plants of the same groups. The method used, may be applied for a comparison of potential dry matter production between varieties under different environmental conditions.