Fifteen cases of the decay of Pu-236 accompanied by the emission of magnesium nuclei were recorded. The probability of this decay mode relative to a decay is (2.7 +/- 0.7) x 10(-14). A partial half-life of (1.25 +/- 0.12) x 10(9) yr was obtained for spontaneous fission of Pu-236. It was shown that the total probability of cluster decay and spontaneous fission for even-even nuclei with 88 less than or equal to Z less than or equal to 100 has a lower limit of approximate to 10(-9) relative to alpha decay. (C) 1995 American Institute of Physics.