The permeability of 5(6)-carboxyfluorescein (CF) through the phospholipid bilayer membranes was measured by using the system in which the CF-containing phospholipid vesicles (liposomes) were suspended in the gas-liquid flow in an external loop airlift bubble column. The airlift was operated at various superficial gas velocities U-G up to 2.4 cm/s at 25 and 40 degrees C. The CF-containing liposomes composed of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) had the nominal diameters of 50, 100, and 200 nm. The 50- and 100-nm liposomes were stable at 40 degrees C for 5 h even at a high U-G value of 2.4 cm/s based on the observed turbidity of the liposome suspension in the airlift. On the other hand, the 200-nm liposomes were stable at a low U-G value of 1.4 cm/s, although a progressive decrease in size of the liposomes was implied at the high U-G value of 2.4 cm/s. The permeability coefficient P-CF of CF through the lipid membrane of the 100-nm liposomes was significantly increased with increasing U-G at a high temperature of 40 degrees C, while at a low temperature of 25 degrees C the P-CF value was little dependent on U-G. As a typical result on the above liposomes, the P-CF value (9.2 x 10(-11) cm/s) at 40 degrees C and U-G = 2.4 cm/s in the airlift was more than 15 times larger than that at 25 degrees C in the static liquid corresponding to U-G = 0. In addition, the dependence of the P-CF value on U-G at 40 degrees C became more significant with increasing the size of liposomes suspended. The results obtained revealed that the permeability of the liposome membranes could be regulated by suspending the liposomes in the gas-liquid flow in the airlift without modulating the membrane composition of liposomes.