An experimental investigation was conducted to study the effects of some geometric parameters of runners and nozzles (e.g., diameter ratio and throat width ratio) on the efficiency in the cross-flow turbines, by varying of ratio of inner-to-outer diameters of runners and gate openings of two different turbine nozzles under different heads. In this study, four different types of runners (170 mm outer diameter, 114 mm width) were designed and manufactured to investigate the effects of the ratio of inner-to-outer diameters of runners on the turbine efficiency. Each runner had 28 blades and the ratios of inner-to-outer diameters of runners were 0.75, 0.67, 0.58 and 0.54, respectively. The runners were denoted with the numbers 1, 2, 3 and 4, and nozzles A and B. The blade inlet and outlet angles were selected as 30 degrees and 90 degrees. Nozzles A and B were of rectangular cross-sectional channels. Nozzles outlet angles of two solid walls of 16 degrees were measured from the circumferential direction. The performance parameters namely output power, efficiency, runaway speed, reduced speed and power for different nozzle/runner combinations were investigated by changing head range from 8 to 30 m, the nozzle A-runner combinations (A-l, 2, 3, 4) and from 4 to 17 m, the nozzle B-runner combination (B-2) at different gate openings. The results of the present study clearly indicated that there was a negligible difference (e.g., 3% in total between 0.54 and 0.75 diameter ratio) in the efficiency of turbine for different diameter ratios and heads, and that the highest efficiency was obtained as 72% for A-2. (C) 1998 John Wiley & Sons, Ltd.