Chromatographic investigations of Streptomyces ipomoeae infected potato tissue and sweetpotato tissue yielded three compounds which on aseptically cultured minitubers individually reproduced symptoms typical of the common scab disease. Spectroscopic examination of the two minor components elicited sufficient information to identify them as analogs of the major constituent which had been previously characterized as 12-N-methylcyclo-(~-4-nitrotryptophyl-~-phenylalanyl). Subsequent investigations of the infected tissue extracts identified a possible toxin precursor substance as 12-N-methylcyclo-(~-tryptophyl-~-phenylalanyl).