This paper gives some results of experimental investigations of the hydrogen state on iron surface by using secondary ion mass spectrometry (SIMS) method. Emission of negative secondary ions from specimens of technically pure iron, pre-charged electrolytically with hydrogen to concentrations reaching 0.0005wt% (5cm 3 /100g), is studied. It is shown that the abilities to measure negative ion emission extend the analytical capabilities of the SIMS method in the investigation of hydrogen-iron interaction phenomena. The analysis of relationships between the values of secondary ion current and primary ion beam current allows us to distinguish useful hydrogen signals from the background, created by particles adsorbed from the gas phase. As is shown, on the surface of iron the hydrogen atoms, diffusing from a body of iron, can bear a negative charge.