This article reports the first blue/green laser diodes grown on ZnSe substrates. The laser structure employed is a p-on-n separate confinement heterostructure consisting of 0.8-mu m-thick ZnMgSSe cladding layers lattice-matched to ZnSe, 0.1-mu m-thick ZnSe light guiding layers, and a single 60-200-Angstrom-thick ZnCdSe quantum well. Green laser emission (507-517 nm; 2.443-2.394 eV) was observed at temperatures from 77-220 K using cw excitation at 77 K and pulsed excitation (50 ns; 10(-1)-10(-4) duty cycle) at higher temperatures. Blue laser diodes with outputs at 485 nm (2.553 eV) at 77 K have also been fabricated and tested.