To evaluate the actual level of exposure of nonsmokers to tobacco smoke in their living environments, a convenient personal monitor of nicotine specific for tobacco smoke has been developed. The nicotine personal monitor consists of a sampler tube containing 450 mg of Uniport-S coated with silicon OV-17 and a portable sampling pump with a mechanical counter for obtaining total sampling volume. Using the personal monitor attached to a nonsmoker, ambient nicotine was collected in the sampler tube by drawing environmental air at a constant flow rate for a maximum period of 8 hr. The collected nicotine was desorbed by heating and directly transferred onto a GC column with a carrier gas. The amounts of nicotine inhaled by passive smoking in various living environments were estimated to be in the range of 0.9-40 micrograms/hr. These levels are equivalent to those from the active smoking of about 0.001-0.044 ordinary cigarettes in 1 hr.