Self-catalyzed poly(ortho esters) are a new variation of linear poly (otho esters) prepared by the addition of diols to the diketene acetal 3,9-diethylidene-2,4,8,10-tetraoxaspiro[5,5]undecane where dimer segments of lactic or glycolic acid are built into the polymer backbone. By varying the concentration of these segments, polymer erosion rate can be controlled. The present investigation describes the in vitro drug release characteristics from these new polymers. Because poly(otho esters) have potential applications for the delivery of antifibroblastic agents for example after glaucoma-filtering surgery, the in vitro release studies were evaluated using 5-fluorouracil as the active compound. It was shown that a mole ratio of 90/10 or 80/20 diol/diol-lactate lead to a concomitant drug release by diffusion and erosion. It was also shown that the release rate depends on the alkyl chain length of the diol in the polymer backbone but it does not depend on the drug loading.