Local-spin-density-approximation calculations of the magnetic and elec
tronic properties of CoH are reported. In its ground state CoH is foun
d to be a strong ferromagnet with a moment of approximately 1.16mu(B)
and a magnetic energy of 10.1 mRy/fu. The magnetic properties and thei
r relationship to those of Co are discussed in terms of the electronic
structure. The large moment in CoH is explained in terms of proton-in
duced hybridization of the electronic states.