Two Coffea arabica - Hemileia vastatrix incompatible interactions (I-1: coffee cv. Caturra - rust race VI and I-2: coffee cv S4 Agaro - rust race II) and a compatible interaction (coffee cv. Caturra - rust race II) were compared in relation to the infection process and chitinase activity. In the two incompatible interactions the fungus ceased growth in the early infection stages, while in the compatible interaction no fungus growth inhibition was observed. A high constitutive level of chitinase activity was detected in the intercellular fluid of healthy leaves. Upon infection, chitinase isoforms were more abundant in incompatible interactions than in the compatible interaction. Immunodetection showed that class I chitinases are particularly relevant in the incompatible interactions and might participate in the defence response of the coffee plants.