Investigations have been carried out to evaluate the two-phase frictional pressure drop for gas-non-Newtonian liquid flow through helical coils in vertical orientation. The experiments performed using nine coils and four different non-Newtonian liquids. The effects of gas and liquid flow rate, coil diameter, and liquid properties on two-phase frictional pressure drop have been illustrated. An attempt has been made to fit the experimental two-phase frictional pressure drop data by the Lockhart and Martinelli [R.W. Lockhert, R.C. Martinelli, Proposed correlation of data for isothermal two-phase two components flow in pipes, Chem. Eng. Prog. 45 (1949) 39-48] correlation and the modified Lockhart-Martinelli correlation as presented by different authors. In another approach, friction factor method was adopted to correlate the experimental data by dimensional analysis. The correlation developed predicts the two-phase frictional pressure drop with acceptable statistical accuracy. (c) 2007 Elsevier B.V. All rights reserved.