RESUMEN
Effect of three drugs, a pain killer the novalgin, an antibiotic the penicillin and a central system depressant the valium has been studied on the distribution of tryptophan plasma, liver and brain in a desert lizard. Novalgin administration caused a significant increase in a total and free tryptophan concentration in plasma with a considerable fall in total tryptophan concentration in liver and a little in brain too. The antibiotic penicillin caused an increase in total and free tryptophan concentration in plasma and an increase in total tryptophan concentration in liver and brain. An intraperitoneal injection of valium decreased total tryptophan concentration in plasma and liver but there was a significant rise of total tryptophan concentration in brain due to an increase in free tryptophan concentration in plasma