  We report detection of differential rotation on the F5 dwarf psi Cap using
line profile analysis. The Fourier transform of both FeI lambda 5775 and SiI
lambda 5772 are used to obtain a projected rotational velocity of v sini =
(42+-1)km/s. Modelling of the Fourier transformed profiles shows that the
combined effects of equatorial velocity, inclination and differential rotation
dominate the line profile while limb darkening and turbulence velocities have
only minor effects. Rigid rotation is shown to be inconsistent with the
measured profiles. Modelling the line profiles analogous to solar differential
rotation we find a differential rotation parameter of alpha = 0.15+-0.1
(15+-10%) comparable to the solar case. To our knowledge this is the first
successful measurement of differential rotation through line profile analysis.
