Abstract: A method for controlling the release of durgs or other passenger molecules form carrier conjugates, and a class of conjugates that releases drugs when ingested by a cell or subjected to acidic conditions, are disclosed. These conjugates contain a passenger molecule which is attached to a spacer molecule through an acidic bonding group, such as carboxyl, that is in a "cis" configuration with another acidic group, and a carrier molecule that is bonded to the spacer molecule at another site. When subjected to a mild increase in acidity, such as occurs within a lysosome of a cell, the drug or other passenger molecule is hydrolyzed from the the conjugate and released in unmodified, active form.

Abstract: A method of effecting cellular uptake of molecules which are either excluded from cells or poorly transported into cells is disclosed wherein such molecules are covalently bonded to a cationic polymer which serves as a transport carrier to transport the molecules into cells.