The oxygen consumption of Nephrops norvegicus animals collected from the upper continental slope (400 m depth) in the northwestern Mediterranean was monitored under constant conditions of darkness and temperature. Two experiments were performed starting at the beginning of the expected day and at the beginning of the expected night phases, respectively. Mean oxygen consumption values recorded during the expected night were significantly higher than those recorded during the expected day. The slopes of the time series of oxygen consumption data of the two experiments were recalculated in consecutive 1-h intervals, being then averaged for corresponding 1-h time intervals. The plotting over a 24-h cycle of these mean hourly-values revealed a global nocturnal increase in the oxygen consumption in the laboratory. This result is discussed and compared with previously reported catch patterns accounting for emergence from burrows in the field, and locomotor and cardiac activity rhythms recorded in constant conditions in the laboratory in animals from the same depth.