Rotationally resolved electronic spectroscopy in the gas phase, in the absence and presence of an applied electric field, has been used to distinguish the two conformers of 3-aminophenol (3AP) on the basis of differences in their electric dipole moments. cis-3AP has mu = 2.3 D, and trans-3AP has mu = 0.7 D, in their ground electronic states. The two observed values are approximately equal to those expected on the basis of bond dipole additivity rules. However, these rules fail to predict the large change in both the magnitude and the orientation of mu when the two conformers of 3AP absorb light. cis-3AP has mu = 3.3 D, and trans-3AP has mu = 1.7 D, in their excited S, electronic states; the angles of orientation of mu with respect to the a inertial axis change by 13degrees and 38degrees, respectively. This effect is attributed to L-1(b)/L-1(a) state mixing in the S-1 state.