Abstract: A method for reducing aggregation of insulin within aqueous insulin solutions comprising including in said insulin solutions an anti-aggregation agent selected from pharmaceutically acceptable organic compounds having at least two carboxylic acid moieties and at least one amino, or amino derived, moiety. Such insulin solutions with the anti-aggregation agent are also maintained at pH's approximating the isoelectric point of the anti-aggregation agent. Glutamic acid or aspartic acid are especially preferred as the anti-aggregation agent. Relatively small quantities of such agents prevent, or greatly reduce aggregation of insulin even when such insulin solutions are maintained at elevated temperatures and under agitation for extended periods of time.