The development of high-pressure technology has in recent years permitted obtaining extensive new information on the properties of hydrides of group VI--VIII transition metals. In this review, the experimental procedures for compressing macroscopic quantities of hydrogen to record high pressures, phase transitions, and structures of new high-pressure phases in Me–H systems are briefly described. Special attention is devoted to the magnetic properties of solid solutions of hydrogen in 3d metals and their alloys, whose study has yielded definite conclusions concerning the effect of hydrogen on the band structure and exchange interaction in these materials. The role of structural instabilities in the formation of superconducting properties of hydrogen solutions in 4d metal alloys based on palladium is examined.