The influences of some formulation variables and manufacturing processes of the release rates of propranolol from gelation of hydroxypropylmethylcellulose (HPMC) matrices tablets were investigated. The amount of propranolol was determined by UV-Vis spectroscopy at 290 nm. The effects of extended release of matrices tablets were evaluated by the in vitro dissolution test and were compared to the United States Pharmacopoeia (USP) monograph specifications. The results showed that the lowest viscosity grade of HPMC (Metolose 4000) used gave the least burst effect in the earlier stage. The drug/Metolose ratio was an important influence on the drug release; increasing the polymer content decreased the dissolution rate of the drug. The release rate was increased with increase in the tablet content of avicel. The release curve of experimental formulation with 17% avicel was optimal compared with the USP monograph specification; there was no burst effect in the earlier stage (the release percent at 1.5 h was 26.6%) and almost total drug was released from matrices tablet after 24 h (97.4%). The other factors such as lubricant level (0.5 to 2.0%), compaction pressure (100 to 200 kPa), brand of HPMC (HPMC 4000 from Shin Etsu or Methocel K4MP from Dow Chemical Co.), and manufacturing process (tabletted from wet-massed granules or by direct compression) appeared not to modify release rates. (C) 2004 Wiley Periodicals, Inc.