For 40 years, hair tests have been presented as the best approach to document longterm consumption of a drug. This unique property has found numerous applications in clinical, forensic, and occupational toxicology. However, since the beginning of its implementation in biology, external contamination, with an associated risk of false positive result, has been presented as the key in the final interpretation. Evidence of environmental contamination and subsequent health issues can be the task of any toxicologist. Because of recent progress of analytical equipment, it is now possible to quantify drugs in hair with high level of accuracy and specificity at the pg/mg range. Therefore, segmental hair tests can be used to document environmental contamination and are the objective of this publication. In a family law case, N,N-dimethyltryptamine (DMT), a powerful hallucinogen, has been found in the hair of the partner of a repetitive DMT smoker at 4 to 13 pg/mg in 6 × 1 cm segments, with a regular increase of concentrations from the proximal to the distal hair end. The low measured concentrations and the particular pattern of DMT distribution along the hair shaft seem to be typical of environmental contamination, the older hair (those of the distal part) being for a longer time in contact with the drug. Despite strong decontamination, drugs from the environment can remain bound to the hair matrix and therefore be able to be used to document environmental contamination.