[en] The 5s²5p ²P(3/2) - 5s²ns²S(1/2), 5s²nd²D(3/2,5/2) Rydberg series (25 <= n <= 107) in indium have been investigated with high precision. The atoms were excited in an atomic beam by a frequency-doubled pulsed dye laser (lambda approx. 225 nm). The highly excited atoms were detected using the field ionization technique. The ionization limit has been determined at 46 670.107 +- 0.010 cm^-1 from the ²S series. The perturbation of the ²D series due to configuration interaction with the ²D term of the 5s5p² configuration has been studied. Discrepancies with previous observations of these series are discussed. The fine structure splitting of the ²D levels could be determined up to n = 70. It is found to be almost proportional to nsup(*)^-3 over the range observed, but the size of the splitting is strongly affected by the perturbation. A description of the effects is presented in the framework of perturbation theory with Hartree-Fock values as a first order approximation. Level values for the 5s5p²²D(3/2,5/2) levels are predicted and compared with observations. (orig.)