Within a study of the temperature dependence of NQR frequencies in some s-triazine derivatives [1], resonance frequencies at 4.2 K were determined in melamine, cyanuric acid, and cyanuric chloride. New lines, which were not reported so far, were detected in two of these compounds. In melamine, nine more lines were found as already described in [4], In cyanuric chloride, two more lines were found showing a second nitrogen site, in agreement with the existence of two chlorine NQR sites in this compound.