The in vivo and in vitro degradation behavior of poly(trimethylene carbonate) (PTMC) polymers with number average molecular weights of 69 x 10(3), 89 x 10(3), 291 x 10(3) and 457 x 10(3)g/mol (respectively abbreviated as PTMC(69), PTMC(89), PTMC(291) and PTMC(457)) was investigated in detail. PTMC rods (3mm in diameter and 4mm in length) implanted in the femur and tibia of rabbits degraded by surface erosion. The mass loss of high molecular weight PTMC(457) specimens was 60wt% in 8 wks, whereas the mass loss of the lower molecular weight PTMC(89) specimens in the same period was 3 times lower. PTMC discs of different molecular weights immersed in lipase solutions (lipase from Thermomyces lanuginosus) degraded by surface erosion as well. The mass and thickness of high molecular weight PTMC(291) discs decreased linearly in time with an erosion rate of 6.7 microm/d. The erosion rate of the lower molecular weight PTMC(69) specimens was only 1.4mum/d. It is suggested that the more hydrophilic surface of the PTMC(69) specimens prevents the enzyme from acquiring a (hyper)active conformation. When PTMC discs were immersed in media varying in pH from 1 to 13, the non-enzymatic hydrolysis was extremely slow for both the high and low molecular weight samples. It can be concluded that enzymatic degradation plays an important role in the surface erosion of PTMC in vivo.