Thirty-eight cultures of rhizobia and 10 non-rhizobia growing in the root zone of clover (Trifolium glomeratum L.), 5 rhizobia and 3 non-rhizobia in that of lucerne (Medicago sativa L.), and 8 rhizobia in that ofSiratro (Phaseolus atropurpureus DO.) revealed a specific relationship between bacteria and host that determined the kind and degree of deformation of the root hairs.