1 The pharmacokinetics of sodium cromoglycate in four healthy volunteers after slow intravenous infusion have been evaluated following measurement of plasma concentrations by radioimmunoassay. The results confirm earlier findings that sodium cromoglycate is rapidly eliminated from the body and that the data can be fitted to a two compartment open model. 2 The pharmacokinetic parameters derived from the intravenous administration were used to evaluate the pharmacokinetics after inhalation administration via the Spinhaler. A model for absorption from the lungs is described which involves absorption at two different rates; this gives a better fit to the observed data than a single absorption rate.3 A fast absorption rate constant with a mean value of 0.54 min-' and a slower rate constant with a mean value of 0.0097 min-' were found. Of a mean total of 2.84 mg absorbed from a 20 mg inhaled dose, 0.68 ± 0.15 (s.e. mean) mg were absorbed at the fast rate and 2.17 ± 0.37 mg at the slower rate. These rates probably reflect absorption from different sites within the lungs. 4 The results may have important implications for interpretation of clinical findings.