The effects of storage temperature on the diametral compression strength of .delta.-phenylbutazone and barbital (form II) tablets and on the drug dissolution rate were examined. For .delta.-phenylbutazone, it was found that the diametral compression strength, .sigma., increased but the specific surface area, Sw, decreased at high storage temperature. The dissolution rate showed a sharp decrease above 70.degree. C. When the diametral compression strength, .sigma., was plotted against the rate of decrease in the specific surface area for phenylbutazone, a good linear relationship was observed. These findings can be explained by the sintering mechanism. In the case of barbital (form II), .sigma. decreased and the dissolution rate increased at high temperatures. The specific surface area, Sw, however, exhibited no significant change with storage temperature. Barbital does not appear to exhibit extensive sintering and the main mechanism involved is polymorphic transition.