Alteration of pharmacokinetics of proteins by charge modification

There is disclosed charge-modified conjugates comprising a targeting protein bound to a therapeutic or diagnostic agent. Charge-modifying a conjugate to cause an acidic shift in the isoelectric point results in prolonged serum half-life upon in vivo administration and is useful to accumulate a therapeutic agent at the target site. Conversely, charge-modification to cause a basic shift in the isoelectric point of the conjugate reduces serum half-life upon in vivo use for diagnostic imaging purposes and results in higher target-to-background ratios.