Fifty-eight boars of the “German Landrace” breed were fattened between 70 and 110 kg in individual housing at ambient temperatures of 15°C or 35°C with 60% relative humidity in both cases. The animals under warm conditions showed increased growth of the skeleton and reduced growth of the heart, liver, kidneys, spleen and stomach. The feed intake was strongly restricted by the high temperature, while water consumption showed an extremely high variance. Correspondingly the daily gains were strongly depressed, although the feed conversion ratios of the warm- and cold-housed animals were not significantly different. The fat thickness of the warm-housed animals was significantly lower.