  We present new Space Telescope Imaging Spectrograph (STIS) observations of
three spiral galaxies, NGC 4303, NGC 3310 and NGC 4258. The bright optical
emission lines H$\alpha$ $\lambda$ $6564 \AA$, [NII] $\lambda$$\lambda$
$6549,6585 \AA$ and [SII] $\lambda$$\lambda$ $ 6718,6732 \AA$ were used to
study the kinematics of the ionized gas in the nuclear region of each galaxy
with a $\sim 0.07\arcsec$ spatial resolution. In NGC 3310, the observed gas
kinematics is well matched by a circularly rotating disk model but we are only
able to set an upper limit to the BH mass which, taking into account the
allowed disk inclinations, varies in the range $5.0 \times 10^{6} - 4.2 \times
10^{7} M_{\odot}$ at the 95% confidence level. In NGC 4303 the kinematical data
require the presence of a BH with mass $M_{BH}=(5.0)^{+0.87}_{-2.26}\times
10^{6}M_{\odot}$ (for a disk inclination $i=70$ deg).In NGC 4258, the observed
kinematics require the presence of a black hole with $M_{BH}=
(7.9)^{+6.2}_{-3.5} \times 10^{7}M_{\odot}$ ($i=60$ deg). This result is in
good agreement with the published value $(3.9 \pm 0.1) \times 10^{7}
M_{\odot}$, derived from $H_{2}O$-maser observations. Our attempt at measuring
BH masses in these 3 late type Sbc spiral galaxies has shown that these
measurements are very challenging and at the limit of the highest spatial
resolution currently available. Nonetheless our estimates are in good agreement
with the scaling relations between black holes and their host spheroids
suggesting that (i) they are reliable and (ii) black holes in spiral galaxies
follows the same scaling relations as those in more massive early-type
galaxies. A crucial test for the gas kinematical method, the correct recovery
of the known BH mass in NGC 4258, has been successful. [abridged]
