The total glycoalkaloid concentrations in aerial and subterranean tubers of 14 potato genotypes were measured using high-performance liquid chromatography immediately after harvest. Post-harvest, aerial tubers from all genotypes were exposed to 144 h continuous fluorescent light; additionally three genotypes (cvs Home Guard, Kerrs Pink and Desiree) were subjected to mechanical wounding prior to glycoalkaloid analysis. Variations in glycoalkaloid concentrations between aerial tubers taken from a single genotype (cv Kerrs Pink) were determined by analysis of eight aerial tubers formed in the second leaf axil, selected from separate individual plants. Irrespective of genotype, total and individual glycoalkaloid concentrations were higher in aerial than in subterranean tubers. The highest glycoalkaloid concentrations were found in aerial tubers of cv Kerrs Pink (1343.0 mg kg-' FW) and lowest in cv Lindsey (301.0 mg kg-' FW). Ratios of a-chaconine: a-solanine in aerial tubers differed significantly (P < 0.05) from those in subterranean tubers of cv Cara, Golden Wonder, Home Guard, Lindsey, Maris Piper, Record and 8859 indicating that exposure to light during aerial tuber growth enhanced the synthesis of one glycoalkaloid to a greater degree than the other. In all cultivars except cv Maris Piper, exposure of aerial tubers to 144 h continuous fluorescent light postharvest increased total and individual glycoalkaloids compared with darktreated controls. However, the ratios of a-chaconine : a-solanine in all genotypes except cv Golden Wonder (decreased a-chaconine: a-solanine, P < 0.05) were not significantly altered in comparison with dark controls, indicating that light exposure of aerial tubers post-harvest fails to enhance selectively synthesis of individual glycoalkaloids in the majority of cultivars. Regardless of cultivar, total glycoalkaloid, a-solanine and a-chaconine concentrations were higher in wounded than unwounded aerial tubers. Wounding stimulated synthesis of a- solanine more than a-chaconine (P < 0.05) in cv Home Guard and Desiree. Glycoalkaloid concentrations in aerial tubers varied widely from a minimum of 1010 mg kg-' to a maximum of 2520 mg kg-' FW when harvested from individual plants of cv Kerrs Pink but selected from equivalent positions on the plant. Throughout the experiments large, non-significant increases in total and individual glycoalkaloid concentrations were recorded following light and wounding treatments. The scientific implications of aerial tuber formation are discussed.