A thermoelectric “nano-nose” has been built from tangled bundles of single- walled carbon nanotubes (SWNT). The detector's thermoelectric response [.Delta]S is sensitive to the logarithmic energy derivative of the additional bundle resistivity ([.rho]a) which is identified with the adsorbed molecules. The response is therefore specific to the details of the interaction of the adsorbed molecule with the nanotube wall; even gases such as He, N2 and H2 can be easily detected. Plots of [Δ]S vs. [ρ]a are sensitive to whether oxidation or reduction of the tube wall is taking place, and to whether the gas molecule is physisorbed or chemisorbed. The utility of the sensor stems from the amphoteric nature of the SWNT, the quasi-one-dimensional character of the charge conduction and the high specific surface area of SWNTs.