The results of experimental investigations of pressure shifts and broadening of spectral lines of polar molecules performed in the submillimeter region by a microwave spectrometer RAD are reported. About 30 measurements were made of self-shift and foreign gas shift parameters of the lines of NH 3, PH 3, AsH 3, and H 2O molecules including lineshifts in excited vibrational states, lineshifts of transitions connected by common levels, lines with various values of J and K quantum numbers, and the "forbidden" |∆ K| = 3 lines. On the basis of the data obtained in this work and data available in the literature, new experimental dependences of lineshifts on molecular parameters are found. The results are well described by a simple "Stark effect" model of lineshifts. Some new directions of investigations are outlined.