The ac magnetic susceptibility of left bracket N(CH//3)//4 right bracket NiBr//3 has been studied as a function of external field. The substance behaves as a metamagnet. Portions of the phase diagram are presented; the best-fit parameters are D/k//B equals 4. 7 K and z prime J prime /k//B equals 0. 032 K. The ratio of interchain to intrachain interactions is 10** minus **2.