Silica gel confirmed its function as viscosity agent for lipophylic excipients for suppositories, ensuring homogeneous drug distribution in the suppository mass. The influence on release rate of a water-soluble drug (benzydamine hydrochloride) was clearly different according to type of silica gel. With Aerosil 200 (hydrophylic), after a progressive decrease in release rate at the lowest concentrations, an increase was observed at the highest concentrations, until it reached that of the suppositories without silica gel. With Aerosil R972, release rate decreased progressively with increased silica gel concentration, until release was practically inhibited even at low concentrations.