IN potato breeding trials conducted here extensive investigations are required to determine the relative resistance of selected seedlings to the common scab disease caused by Streptomyces scabies (Thaxt.) Waksman and Henrici. The tissue-culture technique1,2 for establishing a ready source of aseptic tubers potentially offers a rapid and convenient method for indexing their resistance and for studies on the host–parasite interactions. To evaluate this technique for studies on the common scab disease, tubers were produced in vitro using etiolated stolons1 and aerial stem nodes of greenhouse-grown plants3. White's amended medium, containing 10 per cent sucrose for etiolated sprouts and 8 per cent sucrose for stem nodes, was used.