The photometric and spectral study of 7 selected planetary nebulae has been carried out since 1968. (See: Mem. Soc. Roy. Sci. Liege, 6
ser., 1973, 5, 473). During nearly 30 years of photoelectric observations, 5 planetaries (NGC 6572, IC 4997, Hu2-1, NGC 6891 and NGC 6543) have undergone noticeable variations of integral UVB-brightness in the range 0.1÷0.6 mag. The nebulae NGC 6720 and IC 3568 showed no changes of integral brightness exceeding 0.1 mag. The most remarkable behaviour was found for the nebula IC 4997: a steady decrease of the integral brightness in 1968–85, amounted on the whole to 0.4 ÷ 0.6 mag., an unexpected stop of this decrease in 1985–86, and almost monotonous brightening in 1987–96.