In a previous paper by Aguillon et al. Powder Technol., 83 (1995) 79, the measurement of solid local fluxes in a pilot circulating fluidized bed (CFB) was discussed. It was shown that suction probes give good results in general only when the suction velocity is set at the gas superficial velocity. In the present work, the solid flux profiles are combined with the local solid velocities obtained by means of an optical probe. The velocities are based on the cross-correlation of two signals obtained from the reflection of light on the particles by the optical probe. The method proposed here explains how to combine the local solid flux and velocity in order to determine the local solid concentration. Solid concentration profiles are determined in a rectangular cold pilot CFB. The results obtained show that the mean solid concentration calculated from the integration of concentration profile on the section of the bed are in good agreement with those measured independently from the pressure drop of the column.