Total solanine determinations were made on tubers of Netted Gem and Irish Cobbler potatoes that were (1) at sprouting and at fully resting metabolic stages; (2) illuminated with 15 w. and 150 w. incandescent light sources for 0 to 48 hours at 6-hour intervals; and (3) exposed to temperatures of 4 °C. and 12 °C. during the light treatments. Varietal differences in response were noted. Exposures longer than 6 hours made little change in solanine build-up, and the light treatments produced more effect than did the temperatures used. Sprouting tubers of Irish Cobbler showed a significant decrease in glycoalkaloid content; but under the same temperature and light conditions resting tubers of this variety showed a slight increase. Sprouting Netted Gem tubers showed little change after treatment, whereas in the dormant stage the solanine content decreased slightly under low light and increased after exposure to the 150 w. light source.