Biocompatible non-toxic triblock copolymers having an A-B-A structure wherein each A is a hydrophilic, biocompatible end block and the B middle block is a hydrophobic desaminotyrosyl tyrosine polycarbonate or polyarylate. The copolymers spontaneously self-assemble to form low critical aggregation concentration nanospheres having utility as delivery vehicles for hydrophobic biologically or pharmaceutically active compounds.