INTRODUCTION: In the present paper, we study the urinary excretion of tryptophan metabolites, in both the kynurenine and melatonin pathways in pediatrics patients with febrile and epileptic convulsions. MATERIAL AND METHODS: The patients were classified as follows: GC (Control group, n = 39); FCG (Febrile convulsion group, n = 51); ECG (Epileptic convulsion group, n = 28). Taking into account the existence of a circadian rhythm in melatonin secretion, the groups were further divided into two subgroups (Day (9.00-21.00)/Night (21.00-9.00). Melatonin was measured by RIA, while urine metabolites were measured by thin-layer chromatography. Statistical analyses included a two way ANOVA and comparison of the results. ABREVIATIONS: KYN: L-Kynurenine, 3-OHA: 3-OH-anthranilic, AX: xanturenic acid, OH-K: 3-OH-Kynurenine, AK: Kynurenic Acid, aMT: Melatonin, Trp: tryptophan. CONCLUSIONS: 1.- Normal children showed a circadian variation in patterns of elimination of some of metabolites of tryptophan via the kynurenin pathway and a close correlation between theese and methoxy - indoles pathway. 3.- In the presence of convulsive crises this correlation disappears enterely probably because of the need to cover more demanding biological requirements and clearly modify the pattern of elimination of some Trp metabolites.