The invention provides methods of screening agents, conjugates or conjugate moieties, linked or linkable to agents, for capacity to be transported as substrates through the PEPT2 transporter. The invention also provides methods of treatment involving delivery of agents that either alone, or as a result of linkage to a conjugate moiety, are substrates of the PEPT2 transporter. The invention also provides conjugates comprising a pharmaceutical agent which is linked to a conjugate moiety that is a substrate for a PEPT2 transporter.