The operational behaviour of hydraulic and mechanical systems in subzero temperatures is of considerable interest to manufacturers and operators of mobile and earthmoving machines which work in extremely cold climatic conditions. The majority of such machines are designed for operation in moderate climatic conditions and will have to be specially adapted for working in very low temperatures. The adaptation of such machines to operation in subzero temperatures and verification of their operational limits may be very expensive as it usually requires field testing. To carry out such tests the machines and test equipment must be transported to a low temperature zone. The conduct of tests is weather dependent and only limited modifications to machines are possible under field conditions. This paper describes the environmental facility for full scale, subzero temperature, testing of mobile and earthmoving machines which may help to shorten considerably the development cycle and be less expensive than field trials. Selected results of tests on the hydraulic systems of mobile cranes are presented and discussed.