Respiration and calcification were investigated in the ectocochleate cephalopod Nautilus macromphalus Sowerby. Specimens were collected off New Caledonia, in October 1991, and kept at the Noumea Aquarium until December 1991. The respiratory quotient and calcification rate of 5 individuals were measured during 14 short term incubations (63 to 363 min). Oxygen uptake was recorded with a polarographic oxygen sensor. CO2 flux and calcification were calculated from changes in pH and alkalinity (alkalinity-anomaly technique). Several methods were used to compute the respiratory quotient (RQ); a functional regression indicated an RQ of 0.74. CaCO3 exchange rates were linearly related to respiratory quotient, calcification occurring in individuals with a low RQ. CaCO3 uptake from the surrounding water was noncontinuous. From the highest CaCO3 uptake, maximum growth rate was estimated as 7.1 mg shell wt h- (=61 g yr-1).