During the first 10 d of a total fast the changes in a series of cognitive parameters: short-term memory, long-term memory, speed of information processing, vigilance, and mental control were tested in 14 obese inpatients and compared with a control group. Ten days of fasting induced no detrimental changes. An improvement in the subtest 'Repetition of digits' was interpreted as improved motivation as a consequence of successful weight reduction. In contrast to the experience of normal weight people during famine periods, obese patients seem to tolerate short-term fasting periods without negative intellectual effects.