[en] For the purpose of getting more detailed information concerning the processes leading to statistical fluctuations of an ionization chamber current, measurements with various radioactive sources have been done. By using the experimental arrangement described elsewhere [A. Necula et al. Nucl. Instr. and Meth. A 332 (1993) 501] the mean value and the standard deviation of the ionization current for ³H (water vapours), ⁶⁰Co (sealed source), ⁸⁵Kr (gas), ²⁰⁴Tl (8 mm diameter disk) and ²³⁹Pu (10 mm diameter disk), beta, gamma and alpha sources have been measured. A statistical model explaining the experimental data is proposed. ((orig.))