Microbial abundance in orchid rhizoplane differed on two investigated plants. Thus, 1 g of terrestrial P. appletonianum roots was populated by 3.5±0.18×106 bacteria, whereas 1 g of epiphytic P. articulata roots – by 192±8.5×106 bacteria. This finding corresponds to our previous results on greenhouse Acampe papillosa Lindl. Associative bacteria populated its aerial roots 30 times more densely than its substrate roots ( Tsavkelova et al., 2004). Thus, the aerial roots may serve as a favorable habitat for bacteria due to the presence of the spongy velamen.