Observations were made with standard varieties and new clones of Irish potatoes (Solatium tuberosum L.) to determine the localization of internal brown spots ("Chocolate" disease) in the tubers. This disease is considered to be of physiological origin, and an attempt was made to correlate the internal brown spots with external characteristics of the tubers, such as size, shape, roughness of skin, and the presence of necrosis in young sprouts. The following results were obtained : a) the presence of internal brown spots appears to be closely related to the variety and weather conditions during the growing season ; varieties such as Konsuragis and Ultimus give high percentages of internal brown spots when grown in the socalled rainy season (September to February). They do not show these symptoms in the dry season (March to August) or under well controlled irrigation ; b) internal brown spots have been found to appear more frequently in the apex and middle of the tubers than in their base; c) a high correlation between rough skin and the presence of the disease in the tubers was noticed for varieties that have a tendency to show internal brown spots ; this was noticed even in case of tubers that due to unfavorable weather conditions showed two distinct phases of growth, one with a rough skin and the other with a smooth one ; brown spots could be seen only in the flash of that part of the tuber that had a rough skin ; d) in some instances the presence of necrosis in the young sprouts was also correlated with the presence of internal brown spots in the tubers e) potato tubers affected with the "chocolate" disease are hard and unfit for human consumption.