We observed the low-mass X-ray binary and Z source GX 17+2 with the Ro
ssi X-Ray Timing Explorer during 1997 February 6-8, April 1-4, and Jul
y 26-27. The X-ray color-color diagram shows a clear Z track. Two simu
ltaneous kHz quasi-periodic oscillations (QPOs) are present in each ob
servation, whose frequencies are well correlated with the position of
the source on the Z track. At the left end of the horizontal branch (H
B), only the higher frequency peak is observed, at 645 +/- 9 Hz, with
an rms amplitude of 5.7% +/- 0.5% and an FWHM of 183 +/- 35 Hz. When t
he source moves down the Z track to the upper normal branch, the frequ
ency of the kHz QPO increases to 1087 +/- 12 Hz, and the rms amplitude
and FWHM decrease by a factor of 2. Farther down the Z track, the QPO
becomes undetectable, with rms upper limits typically of 2.0%. Halfwa
y down the HB, a second QPO appears in the power spectra with a freque
ncy of 480 +/- 23 Hz. The frequency of this QPO also increases when th
e source moves along the Z track, up to 781 +/- 11 Hz halfway down the
normal branch, while the rms amplitude and FWHM stay approximately co
nstant at 2.5% and 70 Hz. The QPO frequency difference is constant at
293.5 +/- 7.5 Hz. Simultaneously with the kHz QPOs, we detect HB QPOs
(HBOs). The simultaneous presence of HBOs and kHz QPOs excludes the ma
gnetospheric beat-frequency model as the explanation for at least one
of these two phenomena.