ABSTRACT The ethnobotanical literature lacks joint analyses of the factors that may influence the differential use of medicinal plants. This study intends to fill that void by evaluating the local criteria for the differential use of medicinal plants in a rural community in Northeastern Brazil. We chose two health problems (influenza and constipation) characterized as diseases by local (emic) classification to address the following hypotheses: (1) the most important medicinal plants are easier to acquire; (2) the most important medicinal plants are perceived as being more efficient; and (3) the most important medicinal plants taste better (greater palatability). The plants mentioned in interviews were ranked according to the perception of their use (dependent variable), the difficulty of their acquisition, their taste and their efficiency (independent variables). The perceived efficiency explained the use of medicinal plants for both diseases, while taste explained the use only for constipation. The final models for ‘influenza’ contained only efficiency, while those for ‘constipation’ contained all three variables. These findings indicate that medicinal categories many not be homogeneous and that different targets may be influenced by different variables.