Contrary to the elution pattern of bovine eye lens proteins chromatographed on a TSK GEL G5000 PW type column, an additional peak, representing 4.10 6 dalton aggregates, was observed on a combined G5000 PW–G4000 SW type system. This extra peak, found between the G5000 PW total exclusion fraction and α-crystallin (M r 1.1 · 10 6), appeared to correspond to the G4000 SW void volume. Simulation calculations substantiated that this peak is the result of coupling the two columns and does not originate from a distinct sub-population of molecules. Such artificial peaks may be expected whenever a broad molecular weight distribution extends beyond the fractionation limits of at least one of the constituents of a combined gel permeation system. It is inferred that the hypothetical exclusion limit for compact, globular, symmetrical proteins on TSK GEL G5000 PW is near 10 8 dalton.