The optothermal technique has been utilized to obtain the first high resolution spectrum of pyridine in the region of the S-1<--S-0 electronic transition. Rotational profiles for several vibronic bands (0(0)(0), 6a(0)(1), 16b(0)(2)6a(0)(1), 6a(0)(2), 12(0)(1)) were measured and found to be severely homogeneously broadened with linewidths of the order of 3-5 GHz, in agreement with previous lifetime measurements. Rotational constants of pyridine in the excited S-1 vibronic levels were extracted by a band contour analysis. The values obtained are in good agreement with results from ab initio calculations, also presented here. (C) 1997 American Institute of Physics.