  We present the most general rotating black hole solution of five-dimensional
N=4 superstring vacua that conforms to the ``no hair theorem''. It is chosen to
be parameterized in terms of massless fields of the toroidally compactified
heterotic string. The solutions are obtained by performing a subset of O(8,24)
transformations, i.e., symmetry transformations of the effective
three-dimensional action for stationary solutions, on the five-dimensional
(neutral) rotating solution parameterized by the mass m and two rotational
parameters $l_1$ and $l_2$. The explicit form of the generating solution is
determined by three $SO(1,1)\subset O(8,24)$ boosts, which specify two electric
charges $Q_1^{(1)}, Q_{2}^{(2)}$ of the Kaluza-Klein and two-form U(1) gauge
fields associated with the same compactified direction, and the charge Q
(electric charge of the vector field, whose field strength is dual to the field
strength of the five-dimensional two-form field). The general solution,
parameterized by 27 charges, two rotational parameters and the ADM mass
compatible with the Bogomol'nyi bound, is obtained by imposing $[SO(5)\times
SO(21)]/[SO(4)\times SO(20)]\subset O(5,21)$ transformations, which do not
affect the five-dimensional space-time. We also analyze the deviations from the
BPS-saturated limit.
