- We investigate the characteristics of the coherent population trapping (CPT) states in a dense medium. We incorporate the local-field effects into the density-matrix equations and numerically integrate the resulting nonlinear equations. We find that the CPT state is essentially unaffected by the local-field effects for all ranges of field strengths; however, states close to the CPT state are sensitive to them. We demonstrate a dispersive behavior near the CPT state in a dense medium besides important asymmetries and shifts of the Autler-Townes peaks in absorption spectra. We also study the effect of local fields on the dynamics before CPT occurs and show that the evolution to the CPT state is delayed due to the local fields. We extend our calculation to analyze lasing without inversion in a dense medium of systems. 1996 The American Physical Society.