Researchers examining the relationships between traditional medicine and biomedicine have observed two conflicting tendencies. Some suggest that the use of biomedicine and biomedical concepts displaces the use of traditional medicine and medical beliefs. Other scholars have found that traditional medicine and biomedicine can co-exist, complement, and blend with each other. In this paper we use an econometric model and quantitative data to test the association between individual knowledge of pharmaceuticals and individual knowledge of medicinal plants. We use data from a survey among 136 household heads living in a rural indigenous community in Oaxaca, Mexico. Data were collected as a part of long term fieldwork conducted between April 2005 and August 2006 and between December 2006 and April 2007. We found a significant positive association between an individual's knowledge of medicinal plants and the same individual's knowledge of pharmaceuticals, as well as between her use of medicinal plants and her use of pharmaceuticals. We also found a negative association between the use of medicinal plants and schooling. Our results suggest that, in the study site, individual knowledge of medicinal plants and individual knowledge of pharmaceuticals co-exist in a way which might be interpreted as complementary. We conclude that social organization involved in the use of medicines from both traditional medicine and biomedicine is of particular significance, as our findings suggest that the use of pharmaceuticals alone is not associated with a decline in knowledge/use of medicinal plants.