Backcross-derived isolines of soybean [Glycine max (L.) Merr.] cultivars with and without the Rps1-k gene for resistance to Phytophthora rot (Pythopthora megasperma f. sp. glycinea) were grown in hydroponic culture with and without metribuzin [4-amino-6-(1,1-dimethylethyl)-3-3(methylthio)-1,2,4-triazin-5(4H)-one] added at 0.15 mg L−1. A marked tolerance to metribuzin was associated with Rps1-k possibly from an allele at the Hm/hm locus which is known to be linked closely with the Rps1 locus. This improved tolerance could reduce the occurrence of injury from metribuzin applications.