Development of Taylor vortices in the well-defined concentrated suspension comprising monodispersed microspheres and water/alcohol mixture was observed by using a transparent cylinder with a rotating inner rod. The critical rate of shear, (D_{\mathrm{cr}}), defined by the onset of the Taylor vortex determined by the stripe formation, tallied well with that of the inflection point detected by the rheological measurement. The correlation between (D_{\mathrm{cr}}) and the solid volume fraction was explained by an empirical flow equation accounting for the interparticle interaction. The relaxation time for the Taylor vortex, (T_{r}), was defined as the time needed for the Taylor vortex to emerge at the rates of shear larger than (D_{\mathrm{cr}}). The change in (T_{\mathrm{r}}) with the rate of shear was expressed as (T_{\mathrm{r}}=\left[\alpha\left(D-D_{\mathrm{cr}}\right)^{n}\right]^{-1}). Variation of the constant (\alpha) with solid volume fraction was similar to that of bulkiness of flocs in the flowing suspension, so that the factor predominating (\alpha) was considered to be the hydrodynamic effective size of the primary or aggregated part icles. (a) 199.1 Acatemic Press, Inc.