the invention discloses a composition having a mixture of a pharmaceutically , medically or veterinarily acceptable polymer , preferable a poly copolymer containing between about 10 and 100 wt . % lactic acid units , preferably between about 50 and 90 wt . % la units , and α -- ω - hydroxypoly . methods of forming solid implants in situ in an animal body , said implants optionally comprising a drug or other biologically active agent , as well as the use of the compositions of the invention in the treatment of animal bodies , are also disclosed .