Diabetic retinopathy (DR) is becoming one of the most important complications of diabetes at present. Endothelin-1 (ET-1) and protein kinase C (PKC) are the two important proteins involved in the pathogenesis of DR. A clarification on the interaction between ET-1 and PKC has not yet been made. Here, the author used a new gene ontology technology to predict the molecular function of ET-1 and PKC in an episode of co-expression. With the use of the GoFigure server, the molecular function of ET-1 and PKC is predicted. According to this study, different pathways can be derived from ET-1 and PKC; however, ET-1-PKC produces the same pathway as PKC. This could mean that the interaction between ET-1 and PKC results in increased activity of the PKC pathway but does not generate any new pathway. This finding can be a good explanation for the co-expression between ET-1 and PKC in the pathogenesis of DR.