The purpose of this research was to study the anti-hyperglycemic effect of 28 medicinal plants used in the treatment of diabetes mellitus. Each plant was processed in the traditional way and intragastrically administered to temporarily hyperglycemic rabbits. The results showed that eight out of the 28 studied plants significantly decrease the hyperglycemic peak and/or the area under the glucose tolerance curve. These plants were: Guazuma ulmifolia, Tournefortia hirsutissima, Lepechinia caulescens, Rhizophora mangle, Musa sapientum, Trigonella foenum graceum, Turnera diffusa, and Euphorbia prostrata. The results suggest the validity of their clinical use in diabetes mellitus control, after their toxicological investigation.