Continuously tunable cw diode lasers that produce narrow‐line (1‐ to 10‐MHz linewidth) radiation in the 3.5‐&mgr;m region have been fabricated from Pb0.98Cd0.02S. Lasers operating at 10–20 K produced more than 1 mW of cw power distributed among several modes which could be tuned continuously > 1 cm−1by adjusting the laser current. A spectral range of 30 cm−1could be covered over the full operating range. Ultrahigh‐resolution (10−5cm−1) spectra of H2CO have been obtained to demonstrate the potential application of these lasers to the identification of organic molecules by spectroscopy of their C&sngbnd;H stretch absorption bands.