The Hydromotor is a novel positive-displacement hydraulic machine, designed for power production from low-head sources. It comprises a pair of interlocking multi-lobed rotors, revolving about parallel axes within a closely-fitting casing. the rotor lobe profiles are of original shape, avoiding the occurrence of hydraulic locking. Laboratory tests are described, on a small prototype machine (rotor diameter 182 mm), with results showing good overall efficiency at head differences below 1 m. The results are generalized in terms of dimensionless parameters, to aid estimation of the performance of machines of any scale. It is indicated that the potential for accessing low-head sources with machines of this type is promising. Applications of the working principle are envisaged also for pumping, including the combination of motor and pump to provide water supply, drawing on hydraulic sources only.