The effect of different levels of diet protein on adult Bufo arenarum liver arginase activity and protein content, plasma urea and urinary profile of nitrogen waste products was estimated. Animals kept under environmental constant conditions were submitted to a nutritional standardization period being fed beef meat daily during four days. Then animals were distributed in three groups: Group 0 (control), that was sampled at the end of the standardization period; Group 1, that was starved for 18 days and Group 2, that was fed daily for 18 days and then sampled. With respect to controls, liver arginase specific activity was significantly lower in starving toads (Group 1); liver protein content was elevated in fasted animals (Group 1) and plasma urea concentration increased in the intensive feeding group (Group 2). Urinary nitrogen end products in animals from both control and experimental groups showed no changes either in their absolute values or in their partition percentage rates.