The behaviour of the nuclear quadrupole resonance (NQR) signals in hexamethylenetetramine (C6H12N4) has been studied using the modified spin-locking multi-pulse (SLMP) technique. As a result a train of spin-echo (SE) signals in,observation windows' between RF pulses of a multi-pulse sequence has been detected. Spin-locking effect has also been observed in such spin-system. The dependence of the effective relaxation time T-2e and the SE signal amplitude on parameters of SLMP sequences have also been investigated which resulted in revealing certain peculiarities in the behaviour of the signals obviously characteristic of a spin-system with axially symmetric electric field gradient tensor. (C) 2002 Elsevier Science B.V. All rights reserved.