Short cut methods of estimating energy expenditure from pulmonary ventilation are examined. Although for any one subject carrying out a particular task, the relationship between his energy expenditure and his ventilation is approximately linear, the equation of the regression line differs from task to task and, for any particular task, from subject to subject. Thus, the estimation of energy expenditure, for the generality of subjects and tasks, from pulmonary ventilation alone, by application of a single simple formula, is seen to be unacceptable as the estimates could be subject to serious error. Analysis of expired air cannot, therefore, be dispensed with but the calculations for estimating energy expenditure in terms of ventilation and the analysis of the expired air, already simplified by Weir, are shown to be even further reducible. A nomogram by which they can be carried out with negligible error is presented. Submitted on March 1, 1962