Acid-polyacrylamide gel electrophoresis (acid-PAGE) was used for analysis of lysozyme-estrone glucuronide conjugates. The resolution of the system allowed the identification of individual conjugate families which differed only in the position of acylation or in the number of estrone glucuronide units. Acid-PAGE was a good alternative to denaturing cation-exchange chromatography for the analysis, separation, and small-scale purification of lysozyme-estrone glucuronide conjugates. It revealed the true order of the relative degree of positive charge on the lysozyme-estrone glucuronide conjugates.