Defined solid angle absolute β counting of thick samples using end-window Geiger-Müller counter is shown to be a useful method in the field of environmentl radioanalysis. Some new proposals in connection with the possibility of the reduction and evaluation of the correction factors for the numerous effects responsible for losses and gains in the β counting rate are made on the basis of a comprehensive review of the literature on this topic. A new formula is proposed in order to evaluate correction factors for internal backscattering within thick samples. The case of the exponential decrease of activity as function of the thickness in filter-type samples is treated.