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l -Dopa and α-methyldopa were attached by an ester linkage to α,β- poly (N- hydroxyethyl)- dl -aspartamide (PHEA), a hydrophilic polymer, previously proposed as a drug carrier. Ester bonding was achieved by means of 1-benzotriazolycarbonyl (Btc) group as both an N-protecting and C-activating group in the starting amino acids. In the same way several simple esters of l -dopa and α-methyldopa were prepared. Release of active substances based on hydrolysis of PHEA adducts was studied in vitro, and the following (pseudo) first order release rate constants for l -dopa and α-methyldopa were obtained, 1.06 × 10−3 and 6.91 × 10−4 min−1, respectively. In addition, characterization of the PHEA- l -dopa adduct was carried out in vivo using an intracerebral microdialysis technique in order to evaluate the prolonged release eventually achieved.