Abstract A review on the phenomenon of controllable hydrogen phase naklep and the prospects of its use in metal science and engineering was published in this journal in 1981. In the review we covered both the scientific and practical aspects of the new experimentally discovered phenomenon of the controllable transition of metals and alloys into a high strength state with special physical properties by charging them with hydrogen and causing α solid solution ⇌ hydride β phase transformations. We called this phenomenon “controllable hydrogen phase naklep” (HPN). The HPN phenomenon has been demonstrated in a limited number of metals and alloys under a variety of conditions. Palladium is the classic material for studying this phenomenon. We assume that HPN is a general phenomenon which may be exploited for many alloy systems. The main idea of this work is to confirm the HPN phenomenon in a specific material, i.e. niobium, which is very sensitive to embrittlement and is not a polymorphic material. This is why there are few possibilities to treat niobium, to change its structure and to improve its properties. First we consider the main features of the HPN phenomenon and the reasons why it is not correct to use the terms “cold work”, “strain hardening”, “cold hardening” and others for this new general phenomenon. Data are given for the special vacuum-hydrogen installation and the experimental technique of hydrogen treatment which causes controllable phase naklep of niobium with its plasticity preserved. This is followed by a review of hydrogen treatment results. The possibilities to have a great variety of structures and mechanical properties of niobium and niobium-hydrogen alloys after hydrogen treatment causing HPN are obvious. Finally, new ideas about the phenomenology and mechanism of the phenomenon are discussed.