Experimental pathogenicity was for the first time demonstrated in a strain of C. lusitaniae of clinical origin by the use of concentrated inocula (5.10(7) Y-shaped cells) and the administration of 4 mg of methylprednisolone acetate i.m. injected 4 days before and 3 days after the inoculation. Counts on malt-agar (fig. 1) in kidney and brain showed a decrease during the first 12 hours, followed by a definite increment in cell number between the first and second day. Clinical tests showed a strong proteinuria, high levels of blood urea and creatinine, and a low GOT increase. Glycemia, GPT, and total serum protein values were normal. Histological examinations of kidney showed a delayed penetration with discrete clumps of Y-shaped cells, inflammatory focuses, and compromised tubules and glomerula (Fig. 2). After 2 weeks of study accumulations of cells followed by degenerative phenomena were seen in the various structures examined. Reparation processes were seldom observed (Fig. 3-4).