There was a decrease in all the biological criteria studied with an increase in dose of gamma rays in the M1 generation. A dose dependent response was observed (seedling shoot length, r = - 0.998; root length, r = - 0.985; and pollen fertility, r = - 0.968) and at higher doses the effect was drastic. The LD50 (dose at which 50% lethality would occur) values for all biological end points were relatively moderate. In the M2 generation, the chlorophyll mutation frequency increased in a linear fashion at low to medium (10-20 kR) and was erratic at higher doses. The chlorophyll mutant spectrum included xantha, albina, viridis, tigrina, light green, and dark green. A dose of more or less 20 kR may prove to be an appropriate for inducing chlorophyll mutations in macrosperma lentils studied.