The hydrogen uptake during steam oxidation of Zircaloy-4 and E110 was investigated in situ in the temperature range of 1,000–1,300C. The procedure to determine hydrogen concentrations from the neutron radiographs measured is explained in detail. Very fast hydrogen absorption (less than 10 s) was observed directly after starting the steam injection. The maximal hydrogen concentration reached increased with increasing temperatures. A slight release of hydrogen was observed after this first fast hydrogen uptake. The hydrogen concentration depended on time with a power of 1/8. An enhanced hydrogen uptake occurred if the oxidation switched into the breakaway mode. The hydrogen concentration increased by nearly one order of magnitude.