Peach (Prunus persica Batsch. ‘Lovell’) seedlings and ‘Marianna 2624’ plum (P. cerasifera Ehrh. X P. munsoniana Wight & Hedr.?) cuttings were budded with ‘Fay Elberta’ peach and ‘Marianna 2624’. Of the 4 combinations only ‘Fay Elberta’/‘Marianna 2624’ showed foliar symptoms indicative of graft incompatibility; those trees budded in mid-March appeared abnormal by early August. Prunasin, the only cyanogenic glycoside detected in both species, accumulated in young scion bark of ‘Marianna 2624’ and peach to nearly equal levels. Amounts of prunasin in leaves and bark of ‘Fay Elberta’ on peach were usually greater than in those on plum. The level in the scion bark of ‘Marianna 2624’ was similar on both rootstocks. In late summer, the quantity of the glucoside in peach scion bark rose above that in corresponding plum bark; however, the prunasin concentration in both leaves and scion bark of ‘Fay Elberta’/‘Marianna 2624’ trees was not correlated with the severity of incompatibility symptoms. The prunasin level in the plum rootstock bark immediately below or 18 cm from the union was unaffected by the scion species or by signs of ill-health in the peach top. Although the rootstock was shown capable of affecting the accumulation of prunasin in scion tissues, the stability of the level of this glucoside in the peach/plum combination suggests that cyanogenesis is not closely linked with their incompatibility.