Some of the He-Ne and He-Xe laser lines in the infrared can be tuned within several gigahertz by applying an axial magnetic field. Stark patterns of vibration-rotation lines of organic molecules were observed at 3.36-, 3.39-, 3.50-, and 5.57-μm wavelengths. With applied Stark fields up to 50 kV/cm, many Stark components were resolved and some of the transitions of H2CO, HDCO, and CH4were definitely assigned. Molecular masers in the far infrared cannot be tuned over any appreciable range, but the Stark effects of the rotation lines of NH3at two fixed far-infrared frequencies of the D2O maser were observed. The observations of a Stark component of theJ = 3 leftarrow 2line at 171.6 μm and the forbidden Stark components of theJ = 6 leftarrow 5line at 84.1 μm are reported.