The Slusher–Hahn technique for detection of nuclear quadrupole transitions of low abundance spins at zero magnetic field is briefly described. Factors affecting the observed line shapes are discussed. The 17O n.q.r. spectra for a variety of substances studied at 77 K are presented. The results for several compounds are discussed in terms of the Townes–Dailey model, which leads to an assignment of oxygen 2p orbital populations.