Nine greenhouse grown Arachis hypogaea lines susceptible or resistant to Cylindrocladium black rot were examined histologically for periderm formation. No differences were observed in the basic formation of original or additional taproot periderms or in the suberization of periderm in susceptible and resistant peanut lines. However, extensive periderm were observed more frequently in resistant lines. Additional phellogens occurred in all parts of the taproot that contained living parenchyma. First order branch roots also produced successive periderms.