Described are conjugates formed by an antibody fragment covalently attached to a non-proteinaceous polymer, wherein the apparent size of the conjugate is at least about 500 kD. The conjugates exhibit substantially improved half-life, mean residence time, and/or clearance rate in circulation as compared to the underivatized parental antibody fragment. Also described are conjugates directed against human vascular endothelial growth factor (VEGF), human p185 receptor-like tyrosine kinase (HER2), human CD20, human CD18, human CD11a, human IgE, human apoptosis receptor-2 (Apo-2), human tumor necrosis factor-.alpha. (TNF-.alpha.), human tissue factor (TF), human .alpha.4.beta.7 integrin, human GPIIb-IIIa integrin, human epidermal growth factor receptor (EGFR), human CD3, and human interleukin-2 receptor .alpha.-chain (TAC) for diagnostic and therapeutic applications.