Abstract: A method is provided for preparing monomeric calicheamicin derivative/carrier conjugates with higher drug loading/yield and decreased aggregation. These conjugates are prepared by incubating a calicheamicin derivative and a proteinaceous carrier in a solution comprising a non-nucleophilic, protein-compatible, buffered solution, a cosolvent selected from the group consisting of propylene glycol, ethanol, DMSO, and combinations thereof, and an additive comprising at least one C.sub.6 -C.sub.18 carboxylic acid having a pH in the range from about 4.0 to 8.5 and at a temperature ranging from about 25.degree. C. to about 37.degree. C. for a period of time ranging from about 15 minutes to about 24 hours, and recovering monomeric calicheamicin derivative/carrier conjugates. Alternatively, the conjugates can be prepared by incubating the calicheamicin derivative and a proteinaceous carrier in a solution comprising a non-nucleophilic, protein-compatible, buffered solution and a cosolvent comprising t-butanol.