Correlations between the initial diffusible hydrogen content of welds measured with the ISO-mercury test and the Osaka University mercury test are discussed. A few factors in the test procedure were found to have a great influence on the determination of the hydrogen content. The result was dependent on the material of the specimen, the degassing temperature prior to the test and the surface condition of the test specimen. The data from the quenched specimens are not truly representative of the hydrogen content responsible for cold cracking. An analytical method for determining the remaining diffusible hydrogen content at 100 °C was also studied. The results show that this analytical method suggested recently by Terasaki et al. is very applicable.