A spray‐drying technique has been investigated which provides a free‐flowing powder with decreased dissolution rate for the medicinal agent when compressed into tablets. The fine powder (10–150 μ) obtained by this process has proved to possess excellent drug distribution and when tableted offers good reproducibility of drug release for consecutive batches. The consistency of the drug‐release pattern is tabulated and the drug‐release phenomena discussed. The effect of aging on the release rate of the sustained‐action tablets has been investigated. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company