The feeding behaviour of medium sized 155.25"27.98 cm, ns8. whiting, Merlangius merlangus, under laboratory conditions was investigated with continuous food availability. This investigation was made using both natural, Sprattus sprattus, and artificial diet which was monitored with a periodogram analysis obtained by a newly developed demand feeding unit. The return of appetite of large whiting 305.85"056.90 cm. was also studied. Medium size whiting consumed 5.29 g wet weight.rday corresponding to 3.41% body weight, approximately three sprats of 1.88 g each. The return of appetite after a single meal was found to follow the gastric emptying curve closely. If food is not offered directly but made available through demand feeding, the whiting feed rhythmically every 21 h.; under these conditions, it was estimated that feeding activity returns when the stomach is 40% full.