In this paper it was given the effect o f p-nitrochlorobenzene (NCB) on the homeostasis quan titative parameters o f cave clays microbial communities from Western Ukraine and Abkhazia (Mushkarova Yama, Kuybushevskaya) and soils o f Ecuador tropical ecosystems. For these microbial communities were determined maximum permissible concentrations and types o f responses on xenobiotic. Microbial communities o f Mushkarova Yama cave clays and rainforest soils o f Ecuador were characterized by the

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... type o f response. Microbial communities ofKuybushevskaya clays and mountain jungles o f Ecuador were characterized by the second type o f response. Maximum permis sible concentration o f NCB fo r Mushkarova Yama was 200 mg/l, fo r the other studied microbial com munities -300 mg/l. It was shown, that microbial communities were not only highly resistant to NCB but also interacted with it by destroying this xenobiotic and decreasing its concentration in 4 times. K e y w o r d s: p-nitrochlorobenzene (NCB), karst caves, Ecuador tropical esosystems, micro bial communities.