Photoeletron emission from various aromatic hydrocarbon crystals has been studied and some of the factors (space charge, sample preparation) which might influence the phtoelectric threshold have been investigated. The longstanding problem of determining the “true” photoelectric threshold is re-examined, and a semi-empirical expression is derived which adequately accounts for the spectral dependence of the photoelectron emission yield, and at the same time determines the threshold. New photoelectric thresholds for a number of anthracene derivatives are also reported.