The resting metabolic expenditure of seven allogeneic marrow transplant patients supported by total parenteral nutrition was monitored by respiratory indirect calorimetry using a portable apparatus with a plexiglass canopy. The averaged measurements of resting metabolic expenditure using indirect calorimetry were highly correlated with calculated basal energy expenditures, ideal body weights, fat-free weights, and actual body weights. No consistent correlation was demonstrated between resting metabolic expenditure and body temperature. It is concluded that indirect calorimetry using a portable system is feasible and that measurements of energy expenditure so obtained correlate well with calculated estimates employing the basal energy expenditure equation.