Affinity electrophoresis with four hydroxypropyl methylcellulose batches. Two of the batches (20 and 22) are known to have a heterogeneous substitution pattern and the other two (21 and 23) a homogeneous substitution pattern. Three CBMs (CBM28, X-2 L110F and CBM4-2) and a negative control (G-4) were run in 17% acrylamide gels containing no or 1 mg/ml HPMC. Also a tandem CBM construct of CBM4-2:CBM4-2 together with a tandem negative control (G-4:G-4) were included in the assay. The retardation of the CBMs is modest but differences in mobility can be seen for CBM4-2 and CBM28 in gels containing HPMC of heterogeneous substitution pattern as compared to in gels with HPMC of homogeneous substitution pattern. The difference in retardation is more distinct for the tandem CBM4-2 construct.