The residence time distribution of large solid particles in fluid suspensions was determined in a tubular continuous processing system. Different flow conditions covering both laminar and transient flow regimes were studied for particles with different diameter and density. Experiments were performed for single particles and for suspensions with 1% v/v concentration. The results showed that even for low particle concentrations, particle interactions promote an increased mean residence time and dispersion. Residence time distribution of mixtures of two different types of particles were also measured for different flow conditions. It was concluded that mixing particles with different characteristics often promotes a decrease both in the mean and minimum residence time of each type of particle, although in some situations the opposite was observed.