Field observations of natural populations of sexually compatible wild and weedy relatives of crop plants can provide useful data for assessing the risk of gene flow to these relatives, and theconsequences of that gene flow. Surveys conducted and samples collected during the summer and fall of 2000 and 2001 allowed an assessment of the opportunity for gene flow, as well as its potential consequences. The data from these field observations were supplemented by plot experiments to assess the relative impact of virus infection on free-living, nontransgenic andtransgenic genotypes of C. pepo.