The present paper addresses gas-liquid-solids hydrodynamic regimes that establish in a lab-scale internal circulation airlift operated at low superficial gas velocity batch-wise with respect to liquid and solid phases. Silica sand and glass beads have been used as bed solids at hold-up ranging between 4 and 12% by volume. Transition conditions between fixed bed, fluidized bed and solids circulation regimes 14 have been assessed by means of analysis of pressure data, both in the time-and frequency-domains. Gas-liquid mass transfer coefficient and liquid circulation velocity have been measured in the fluidized bed and solids circulation regimes. (C) 2003 Elsevier B.V. All rights reserved.