  In this paper we have analyzed 25 Galactic O and early B-stars by means of H
and K band spectroscopy, with the primary goal to investigate to what extent a
lone near-IR spectroscopy is able to recover stellar and wind parameters
derived in the optical. Most of the spectra have been taken with SUBARU IRCS,
at a resolution of 12,000, and with a very high S/N (200 or better). In order
to synthesize the strategic H/He lines, we have used our recent, line-blanketed
version of FASTWIND. First we investigated the predicted behaviour of the
strategic lines. In contradiction to what one expects from the optical in the
O-star regime, almost all photospheric H/HeI/HeII H/K band lines become
stronger if the gravity decreases. Concerning H and HeII, this finding is
related to the behaviour of Stark broadening as a function of electron density,
which in the line cores is different for members of lower (optical) and higher
(IR) series. Regarding HeI, the predicted behaviour is due to some subtle NLTE
effects resulting in a stronger overpopulation of the lower level when the
gravity decreases. For most of our objects, we obtained good fits, except for
the line cores of Br_gamma in early O-stars with significant mass-loss, where
this discrepancy might be an indirect effect of clumping. After having derived
the stellar and wind parameters from the IR, we have compared them to results
from previous optical analyses. Overall, the IR results coincide in most cases
with the optical ones within the typical errors usually quoted for the
corresponding parameters, i.e, an uncertainty in Teff of 5%, in log g of 0.1
dex and in Mdot of 0.2 dex, with lower errors at higher wind densities.
Outliers above the 1-sigma level where found in four cases with respect to log
g and in two cases for Mdot.
