The effects of differentiation, novelty, and difficulty of ability tasks upon electrogastrographic activity of healthy subjects during digestion were investigated. Electrical recording of activity of the stomach by means of surface electrodes was performed in 40 healthy volunteers before and after easy or hard tasks. 20 subjects had to complete puzzles; the others had mental arithmetic. Both groups were matched in terms of scores on easy and difficult tasks. Baseline recordings were performed before each trial. The number of waves with peak amplitude greater than 100 mu v on electrogastrographic recording during each time span was measured, using a visual analysis. There was a significant decrease in number of waves/min, during task performance. A more pronounced decrease was produced by subjects working on puzzles than those working on mental calculation and by subjects working on easy tasks than those working on difficult tasks when the easy preceded the difficult ones. A larger decrease was obtained when the tasks of comparable difficulty were performed first. Emotional correlates such as anger and irritability were suggested to play a role in the interpretation of results.