Differentiation of virus serotypes with capillary zone electrophoresis was demonstrated. For four serotypes of human rhinovirus (HRV2, HRV14, HRV16, HRV49), different electrophoretic mobility was achieved at pH 8.3 (borate/boric acid buffer, 100 mmol/L). Addition of detergent (Triton X- 100-R, deoxycholate, and/or SDS) to the background electrolyte was required for reduction of wall adsorption and improvement of peak shape. A major nonviral contaminant, present in all virus samples, was best separated from the viral peaks with 10 mmol/L SDS as additive. The method allowed detecting serotypes HRV16 and HRV49 in crude, partially purified virus preparations. An infectivity assay carried out off-line with fractions collected at the capillary outlet enabled the sensitive and biospecific identification of the peaks of HRV2 and HRV14.