Experiments conducted in vitro showed that coir [coconut (Cocos nucifera) mesocarp pith] suppressed growth of soilborne plant pathogens. Mycelial growth of Phytophthora capsici on potato dextrose agar (PDA) amended with an unsterilized coir suspension was strongly inhibited regardless of suspension concentration. Growth of P. capsici on PDA amended with a filter-sterilized coir suspension was uninhibited. Growth of Fusarium solani on water agar (WA) amended with unautoclaved coir was completely inhibited. Growth of F. solani on WA amended with autoclaved coir was uninhibited. Aspergillus terreus recovered from coir inhibited mycelial growth of various soilborne pathogens by up to 75%. The results from this study suggest that coir has the ability to suppress soilborne plant pathogens in vitro and this ability is largely due to microorganisms associated with the substrate.