Dyspnoea is one of the earliest symptoms in several conditions, such as heart disease and airway obstruction. However, the early phases of these two conditions are hard to distinguish in a reproducible way. In a population study of the natural history and epidemiology of congestive heart failure a scoring test to differentiate the two conditions was developed. In this report the test is presented and evaluated against various clinical and laboratory measures in 644 men sampled from the general population. The test provides a 'cardiac score' and a 'pulmonary score', both based on history and findings at the physical examination. Men who had pulmonary scores (indicating a pulmonary cause of the dyspnoea) had significantly lower values of spirometry variables but no significant pulmonary congestion at X-ray compared to a reference group (no dyspnoea, no pulmonary scores). Men with cardiac scores had significantly larger hearts and more congestion but no significant change of variables measuring airways obstruction compared to the reference group (no dyspnoea, no cardiac scores). Even though there was a moderate overlap of impaired cardiac and pulmonary function in the dyspnoea group, perhaps due to smoking being a common causal agent, the test appears to differentiate the causes of dyspnoea in a manner similar to clinical evaluation but, in contrast to the latter, in a defined and therefore reproducible way.