The essential oils of three chemotypes of rosemary (Rosmarinus officinalis L.) (Lamiaceae) were investigated in vitro for niticidal activity on Pediculus humanus capitis using two methods: microatmosphere and direct application. The results revealed the potent effectiveness of the oil of chemotype 1 (Rabat origin) using the two techniques mentioned, successively followed by the oils from chemotypes 2 (Errachidia origin) and 3 (Oujda origin). Chemical analysis (GC and GC-MS) of these oils was different. Among the main components identified, alcoholic and ketonic compounds were found the most effective on nits using the two methods. The difference in niticidal activity observed is related either to the technique used and to the chemical composition of the oils tested which is in direct relation to the geographical distribution of these chemotypes.