The vapor pressure of pesticides is an important parameter for predicting the distribution of these substances in the environment. Using the Knudsen effusion technique and highly purified samples of lindane (gamma-1,2,3,4,5,6-hexachlorocyclohexane), a thorough reinvestigation of its vapor pressure has been undertaken. The results obtained are compared with previously published values, some of which show considerable scatter, especially at temperatures of natural field conditions. We consider our data to be sufficiently accurate to be used as reference values, e.g. for calibrating other less direct techniques of vapor pressure measurement. On account of our measurements in the range (292 to 326) K we recommend for lindane the vapor pressure equation In p/Pa = (34.53 +/- 0.21) - (11754 +/- 72)(T/K)(-1).