Kratom (Mitragyna speciosa) is a species of large tree that grows in Southeast Asia and is part of the Rubiaceae family. Its leaves are harvested for their medicinal properties and used for their psychoactive effects. In high dose, above 15 grams, kratom has sedative effects. Kratom contains many biologically active alkaloids, including mitragynine and 7-hydroxymitragynine, which are considered the most important psychoactive component and constituting 66% and 2% of the total alkaloid content. The authors report the cases of two kratom consumers, for whom analyses of hair, nail and kratom pulverized were performed by LC-MS/MS. The psychoactive substances were extracted from 20mg of specimens by extraction at pH 9.5, in presence of mitragynine-d₃ used as internal standard. Analyses confirmed the presence of mitragynine at 9,630, 62 and 49pg/mg in hair (3 segments) and 237pg/mg in fingernails. No 7-hydroxmitragynine was detected. The analysis of pulverized kratom confirmed the presence of mitragynine and 7-hydroxymitragynine at 1.6% and 0.0036%, respectively. Several others peaks were observed during the screening of the kratom product, which could correspond to others alkaloids present in the plant. The interpretation of mitragynine concentrations in hair and nails is difficult to establish since few data are available in the literature concerning hair, and this is the first case of identification and dosage of mitragynine in nails.