The microscopic substantiation of Lupus Erythematosus (LE) Cells constituted the first biological test in diagnosing Systemic Lupus Erythematosus (SLE) in such a way that, time ago, both lupus and other systemic autoimmune diseases were diagnosed clinically, and were not noticed in several patients. The inclusion of searching LE cells in the routine of clinical-pathological tests allowed not only advances in diagnostic, but stimulated the regular investigation on SLE particularly, and on autoimmune diseases in general. The LE cells are the result of antinuclear antibody (ANA) existence directed against the modified or injured nucleus of a lymphocyte together with the complement fixation. This altered nucleus acquires a homogeneous aspect, gets free from the cell and suffers phagocytosis by a polymorphonuclear leucocyte (PMN) with the consequent formation of a huge inclusion body in its interior. The referred nuclear mass is rounded with great volume, its stain is basophilic, homogenous and does not reveal chromatin structure, with a particular cytochemical depolymerized DNA, and eliminating the PMN leucocyte nucleus peripherally. At this report, it is described the finding of LE cells in phlegmon effusion of a canine, male, 3 years old, German Shepherd, that presented persistent hyperthermia (41 ± 1.1°C), normocytic-normochromic regenerative anemia (4% of reticulocytes), thrombocytopenia (68,000 platelets), leucocytosis with left-shift (48,000 leucocytes and 12% of band neutrophils), ulcers at the oral cavity (tongue and lips), non-erosive polyarthritis and phlegmons that started at the pelvic legs and improved for the thoracic legs, humero-radio-ulnar and carpal-metacarpi articulations, sequentially. The search for LE cells may be performed directly from the total blood in which the cells' observation is less common by this technique, or indirectly, from patient serum and at patients presenting several clinical signs, in pleural effusions and in the synovial fluid. At the present case, LE cells were searched from blood, serum and subsequent phlegmon effusions, until that, after many attempts, they were found by the first time at that non-cavitary fluid. It is suggested, so, that LE cells might be searched at all types of humors, secretions and fluids, in canines presenting SLE signs as well as other autoimmune diseases.