Bulk condensation polymerizations of adipic acid and octanediol, catalyzed by Candida antartica Lipase B (CALB), were investigated. The polymers formed by 8 and 24 h polymerizations using CALB immobilized on Accurel and Lewatit had similar molecular weights (e.g., M-n at 24 h approximate to15 000). CALB "free" of the immobilization resin was also active for the polymerization but, relative to its immobilized forms, gave slower chain growth (M-n approximate to 10 000 by 48 h). For all three catalyst systems at degree of polymerization (DP) greater than or equal to 20, dispersity (M-w/M-n) was less than or equal to 1.5. Since random processes of step-growth condensation polymerizations give dispersity values greater than or equal to 2, the dispersity of products obtained using CALB as the catalyst is believed to result from the unique chain length or mass selectivity of the lipase. Gel permeation chromatograms showed that between 15 min and 4 h chain growth occurred rapidly so that the fraction of product with M, values > 2910 increased from 28 to 78%. At 70 degreesC the catalyst activity at 4 h remained unchanged but decreased by 15 and 21% at 24 and 48 h. Unexpectedly, an increase in the concentration of CALB on Lewatit from 0.1 to 1 wt % protein resulted in only a small increase in M. (e.g., at 24 h, 14 500 vs 17 800). However, decrease in the percent protein to 0.5% had a large detrimental effect. Between 65 and 90 degreesC the polymerizations occurred with little dependence on the reaction temperature.