The single-pass gain of 4 · 10−5mole/liter solutions of 3,3′-diethylthiatricarbocyanine iodide (DTTC) in methanol and 3,3′-diethylthiadicarbocyanine iodide (DTDC) in acetone, optically pumped by a giant pulse ruby laser, were measured as a function of pump power, wavelength, and time. The transverse pumping laser pulse was synchronized with a probing pulse from a dye laser. Both low-signal and saturated gain measurements were made in the wavelength range 7860–8066 Å for DTTC and 7059–7412 Å for DTDC dye. The pumping pulse widths at half-power were 15 ± 5 nsec, and the pumping power density was varied over a range of 0–7 MW/cm2. Using a steady-state theory, lifetime and cross sections for excited states