We have been screening tropical and temperate soybean germplasm lines to test for variation in the rate of seed transmission of soybean mosaic virus (SMV). In the course of field screening of 400 tropical soybean lines and varieties with the Illinois 11 severe11 isolate of SMV (SMV-Il-S) we were unable to infect the cultivar 'Buffalo'. Our subsequent studies have shown that Buffalo is i111T1une to most SMV isolates and possesses a hypersensitive form of resistance to the isolates that can infect it. Here we present a preliminary report of our findings.