Laser emission has been obtained in Pb1−xSnxSe diodes withxup to 0.28, and the temperature dependence of the emission has been studied in the range from 1.5 to 100°K. The results strongly support a band model in which the conduction and valence band edge states cross as the Sn content is increased from 0 to 0.28. Forx≤ 0.10, the temperature coefficient of the energy gap is positive whereas forx≥ 0.19, the temperature coefficient is negative as predicted by the band model. Also, the results provide evidence that the energy gap is direct on both sides of the crossover point which at 4.2°K occurs forx≈ 0.15.