SCN-resistant soybean varieties reduce the amount of SCN reproduction that occurs when soybeans are grown. But if resistant soybean varieties are grown repeatedly, an SCN population capable of reproducing readily on the resistant varieties can develop. This is because resistant varieties are not immune; they allow some low level of SCN reproduction. The possibility of SCN populations building up on resistant varieties is especially a concern because almost all resistant soybean varieties have SCN resistance genes from the soybean breeding line PI88788 (see article on newly published list of SCN-resistant soybean varieties for 2007 in this issue).