The species HNCS and NCS have been studied by photoionization mass spectroscopy. The adiabatic ionization potential (IP) of HNCS is less than or equal to 9.92 eV; the shape of the ion yield curve near threshold implies a large change in geometry, perhaps to linear HNCS+. Various appearance potentials (AP) from HNCS are determined by a more objective procedure, from which Delta H-f(o)(HNCS)>29.6 kcal/mol (and very likely greater than or equal to 31.0+/-0.7 kcal/mol) is deduced. The adiabatic IP of NCS is 10.689+/-0.005 eV. This quantity, together with AP(NCS+/HNCS), yields D-0(H-NCS)less than or equal to 97.2+/-0.2 kcal/mol. However, a measurement of the appearance potential of NCS+ from (NCS)(2) results in a still lower value, D-0(H-NCS)less than or equal to 93.3+/-1.1 kcal/mol, and Delta H-o(f0)(NCS) less than or equal to 72.7 +/- 0.8 kcal/mol. Approximate values are obtained for Delta H-f0(o)(HNCS+) and for the proton affinity of NCS.