Results: All cases with epidermal consumption and/or mitoses and nearly half of cases with inflammation, asymmetry and focal loss of maturation was associated with.focal deep dermal HMB-45 positivity. Thirteen cases had an MIB-1 index of ≤1 %. Two of 3 cases with MIB-1 index of >1 % had also HMB-45 positivity and/or inflammation. The case with a MIB-1 index of 8 % was an acral nevus bearing 4 of the evaluated morphological features. Conclusion: Focal deep dermal HMB-45 positivity goes parallel with epidermal consumption and dermal mitoses, mostly used prevailing criteria of malignancy in melanocytic lesions but it's expression is not adequate for diagnosis of melanoma. Low MIB1 index can be a reliable marker of benignity. Objective: Leptospirosis in humans usually courses with hypokalemia and hypomagnesemia, and the putative mechanism may be related to nitric oxide production. Methylene blue is a known inhibitor of inducible nitric oxide synthase, and have beneficial effects on clinical and experimental sepsis. Method: Serum creatinine and ionic changes were evaluated at various time points (4, 8, 16 and 28 days) in hamsters. We also determined the effect of methylene-blue treatment when used as adjuvant therapy combined with a late start of standard antibiotic (ampicillin) treatment. Results: Rather than K and Mg depletion, hyperkalemia and hypermagnesemia were observed during acute infection. These findings are probably associated with an accelerated progression to renal failure, since this model is not feasible to mirror the supportive therapy (including fluid expansion) that retards progression to the oliguric/hyperkalemic state. Infected hamsters at day 8 presented diffuse tubular cell swelling with mild or no nephritis. At days 16 and 28 they showed variable degrees of acute tubular changes, regeneration of tubular epithelia and nephritis. Survival and renal pathology did not differ among different treatment groups. Conclusion: Adjuvant methylene blue had no effect on the survival, renal pathology or Mg and K serum levels during acute-phase leptospirosis in hamsters.