Varietal purity in wheat (Triticum aestivum L.) seed production is necessary for enabling market segregation.  Management of gene flow from herbicide-resistant wheat to jointed goatgrass (Aegilops cylindrica Host.), a serious weed of winter wheat, is also affected by varietal seed purity.  We conducted a survey of certified and farm-saved seed samples using a Clearfield (imidazolinone herbicide-resistant) wheat variety as a marker in 2004 and 2005 in eastern Colorado to determine the ability of the two systems to maintain varietal purity.  Samples of non-Clearfield varieties were taken from certified and farm-saved seed producers who either produced or had never produced Clearfield wheat.  Resistant plants were detected using a seed soaking technique in all four seed lot categories.  The mean percentage of resistant plants in farm-saved seed producer samples with Clearfield history was 0.94%, significantly different from zero (P = 0.0003), and significantly higher (P = 0.004) than the mean of samples from certified seed producers with Clearfield history.  Homozygous resistant plants were detected in certified and farm-saved samples from producers who had never grown Clearfield wheat, suggesting seed mixture had occurred prior to seed lots arriving on farms.  Certified seed producers are more effective at maintaining varietal purity than farm-saved seed producers, which may impact gene flow to jointed goatgrass and wheat exports to regulated markets.