The anterior adult human nasal passage contains hairs which act as a fibrous filter for inhaled particles. Particles which are collected by these hairs are likely removed by physical means and are unable to produce toxic effects in the respiratory tract. Measurements have been made of the anterior nasal passage and nasal hair of an adult Caucasian subject, and calculations have been carried out using fibrous filter theory to determine the deposition efficiency for unit density spherical particles of diameter ranging from 1 nm-40 μm at three steady inspiratory flow rates