The urinary excretion of disodium cromoglycate (DSCG) was used as an index of the amount reaching the lungs in nine normal subjects and in fifteen patients with obstructive airways disease. Vital capacity (VC), forced expiratory volume in one second (FEV1) and peak inspiratory flow rate (PIF) through the spinhaler were also measured. The amount of DSCG detected in urine varied considerably. It was correlated with the physiological measures and with age. The usual DSCG excretion pattern was of a declining excretion rate from 0 to 3 hr following the dose, but certain individuals showed a rise to the second hour, before a fall occurred in the third hour. The occurrence of a rise was associated with a very low reading in the first hour, which in turn was associated with severe obstructive airways disease. Overall, the lowest excretion rates, and the poorest scores for VC, FEV1 and PIF were recorded in a sub-group of five chronic bronchitics, who were also the oldest group. In one chronic bronchitic no drug was detected. The highest excretion rates and best physiological scores were recorded in the normal subjects, who were also the youngest group.