Frequency and temperature dependences of dielectric constant, K, and loss, tan delta, and hence a.c. conductivity, a, have been studied for LiF single crystals under a combination of treatments such as quenching, laser excitation, a.c. field treatment and X-ray irradiation. The measurements were made in the frequency range 10(2)-10(7) Hz and in the temperature range 30-400-degrees-C. The dielectric constant, K, of LiF at 30-degrees-C was found to be 8.4 and to be independent of frequency, while the dielectric loss, tan delta, was below 10(-3) at 10(2) Hz. The results indicate that the different treatments on LiF single crystals increase the room-temperature and also high-temperature K and tan delta values appreciably in the low-frequency region. Log sigma versus 1/T plots at frequency 10(2) Hz give the activation energy for conduction in the intrinsic region as 0.97 eV for as-cleaved LiF; this value was found to decrease in variously treated LiF samples. The different treatments on LiF help to increase the concentration of charged lattice defects which, in turn, increases the K and tan delta values.