The behaviour of nuclear quadrupolar resonance (NQR) signals in hexamethylenetetramine (C6H12N4) was studied using the steady-state free-precession (SSFP) pulse technique. Strong intensity variations of the steady-state signal as a function of the frequency offset and pulse spacing were observed, and these are associated with the interference of free induction decay and spin-echo signals in the steady state. Thus it was shown that the detected NQR signal may contain a spin-echo component, and the axial symmetry of the electric field gradient in the sample is not the reason why spin-echo signals were not observed in conventional pulse experiments for the same type of sample. Experimental results of applying some SSFP pulse sequences for nitrogen-14 NQR in (C6H12N4) are reported.