The study of the distribution of hydrogen in steel ingots, despite its practical importance, has not received due attention from previous workers. Available experimental results are mainly fragmentary and non-systematic, and therefore many disputable opinions exist. Desirous of investigating this problem in greater details, the authors employed several annealed ingots of high chromium steels which were considered to be particularly suitable because they evolved little gas at room temperature and consequently the inherent difficulty to avoid the loss of hydrogen during sampling was, to a very large extent, overcome. For this purpose also, suitable apparatus capable of determining relatively small amount of hydrogen was constructed. The results obtained show that the hydrogen distribution in the annealed ingots follows a significant and regular pattern, thus dismissing certain misgiving conclusions based on contradictory results given by previous workers. Although the average hydrogen content of the anealed ingots amounted to not more than half that of the liquid stael, yet in certain parts of their interior the local hydrogen content was found to be higher than that of the liquid steal. This affirms the existence of hydrogen segregation in steel ingots. Moreover, from maps of hydrogen contour lines drawn for the ingots it can be seen that the regions of the highest hydrogen content roughly coincide with the last solification. Indeed, the effect due to certain external irregularities encountered in the course of solification is detectable rather from the hydrogen maps than by the usual method of macro-etching.In the longitudinal or the transverse direction of the annealed ingots, the general trend of hydrogen variation based on average hydrogen content is shown to be governed by the law of hydrogen diffusion. Further examinations reveal that the ingot structure and its internal porosity exert considerable influence upon the distribution. It is likely that hydrogen diffusion may be faster in columnar crystals than in equi-axed crystal regions. The presence of porosities in ingots seems to retard the removal of hydrogen. Such implications have not been sufficiently realized in the past.Based on the discussion of the experimental results, certain immunizing treatment suitable for preventing hairline cracks in certain types of steel is explained.