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The aim was to investigate differences between morning and evening types in the performance variations during the day of four different tasks: visual search, logic reasoning, spatial reasoning, mathematical reasoning. Twelve morning-, 24 intermediate-, and 12 evening-types took part in six consecutive experimental sessions from 8 a.m. to 11 p.m. at intervals of 3 h, during which they had to carry out the four types of tasks, give an evaluation of their own cognitive efficiency and subjective alertness, and record body temperature. Significantly different circadian trends between morning and evening types emerged only in the visual search task. In the reasoning tasks no significant differences were observed in the whole day, as if tasks requiring a high operational load involved a cognitive and motivational engagement which can compensate, in normal day–night conditions, the efficiency decrease due to alertness …