Summary: Fungal diseases cause appreciable cotton yield loses in Uzbekistan and other cotton producing countries. Phytoalexins are one of the active defense mechanism that plants utilize to protect themselves from attack by pathogens, and indigenous plant species may provide compounds that are more potent than those produced in cotton. Cotton (Gossypium) belongs to the family Malvaceae, and phytoalexins produced by some Malvaceae are structurally related to those in cotton. The introduction into cotton of genes responsible for the synthesis of more potent Malvaceae phytoalexins could significantly increase resistance to fungal pathogens that attack cotton. Others have shown that plant resistance is correlated with the speed with which the plant recognizes the pathogen and the potency of the phytoalexins produced. Herein, we report our search for more potent phytoalexins from several members of the Malvaceae family that are indigenous to Uzbekistan. The plants investigated were Hibiscus trionum, Hibiscus esculentus, Hibiscus manihot, Malva sylvestris, Malva moschata, Malva bucharica, Abutilon theophrasti and Althea rosa. The antifungal activities of the phytoalexins from these plants were assayed against the plant pathogens Verticillium dahliae and Fusarium oxysporum f. sp. vasinfectum. Of the plants investigated, the most resistant were M. sylvestris, H. trionum and H. esculentus. In these plants, the phytoalexins achieved maximal concentration within 24 h after inoculation by pathogen spores. Phytoalexins were extracted from the stems of inoculated plants and isolated by chromatography on a silica column. They were further purified by HPLC. IC50 values were determined on partially pure fractions. Structure elucidation of the most active phytoalexins is currently under way.