By means of an inversion of H and K Ca II line profiles the temperature and electron density in the chromosphere above the umbrae of two sunspots have been estimated. The temperature gradient 5 K km -1 exceeds the corresponding values in both quiet regions and plages. At a height of about 1500 km the umbra becomes hotter than the quiet region. At a temperature of about 10 000 K the temperature gradient increases sharply. The electron density at 1500 km is approximately the same as that in the quiet chromosphere at the same height.

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Based on an extended list of lower main sequence stars from Rutten (1987), the relation between chromospheric activity and Rossby number has been revised. The increased statistics changes the shape of the curve as compared with that of Noyes et al. (1984). The saturation at small Rossby numbers has disappeared. The dependence on Rossby number in the range of very large Rossby numbers has weakened. The standard deviation of the activity indices from the mean curve is about 40%. This scatter of individual stars is not due to differences in the spectral type or age of the stars.