RCCSD(T) calculations combined with large basis sets are employed to obtain the heats of formation of LiOH and LiOH+; in addition, the first adiabatic and vertical ionization energies of LiOH are obtained. Our best values are: DeltaH(f)(LiOH, 0 K) = -57.0+/--0.5 kcal mol(-1) and D-0 = 104+/-1 kcal mol(-1). The ground state of LiOH+ is a quasi-linear Renner-Tefler X(2)Pi state and AIE(LiOH) = 8.91+/-0.03 eV. DeltaH(f)(LiOH+, 0 K) = 148+/-2 kcal mol(-1) and D-0 = 23+/-1 kcal mol(-1). The proton affinity of LiO(X(2)Pi) is derived as 230+/-1 kcal mol(-1). (C) 2002 Elsevier Science B.V. All rights reserved.