The use of long-slit spectroscopy at high spectral and spatial resolution has made it possible to measure gradients of gaseous excitation and also velocity fields in a sample of four bright nuclear starburst galaxies selected from the sample of Balzano (1983). Variations are found not only in the intensity but also in the quality of the emission spectra (line ratios and line widths) of the interstellar gas between regions separated by relatively short distances. The need is stressed for studies with at least the present degree of angular and spectral resolution if physical sense is to be made of the interstellar excitation regimes in external galaxies, as well as to investigate a possible evolutionary link between nuclei of intermediate activity.