Prazosin, an antihypertensive drug with postsynaptic α1-aradrenergic blocking activity, has been coupled to poly-N 5-(3-hydroxypropyl-L-glutamine) (PHPG) via a carbamate linkage. PHPG was activated by p-nitrophenyl chloroformate and then reacted with prazosin to form p(HPG-prazosin carbamate) conjugate. Drug loading was 23.9% (w/w). Activated polymer and conjugates were characterized by infrared spectroscopy and differential scanning calorimetry. In vitro studies proceeded in pH 7.4 isotonic phosphate-buffered saline solution. Prazosin was released at a rate of 0.92 mg/day/100 mg conjugate from p(HPG-prazosin carbamate) particles. In vivo studies were performed with New Zealand White rabbits. P(HPG-prazosin carbamate) conjugate particles (100 mg) were suspended in 2 ml saline and injected subcutaneously into both flanks of rabbits. P(HPG-prazosin carbamate) conjugates, following an initial burst, demonstrated a nearly constant plasma prazosin concentration profile above 2 ng/ml, which was maintained for 10 days.