The effects of gamma irradiation on secondary metabolite production in callus cultures derived from four doses of gamma irradiated seedlings on Andrographis paniculata were studied. The effects of lower doses of gamma irradiation on secondary metabolite production in callus cultures were also examined in Andrographis echiodes, since the seedlings of these species were highly sensitive to higher doses of gamma irradiation. The results of this study indicated that gamma irradiation positively influencedandrographolide production in A.paniculata from the callus cultures. The significant impact of this study was that the callus cultures produced from non-irradiated seedlings showed the absence of andrographolide. The effects of four doses of gamma irradiation on the invitro production of andrographolide from the leaf explants of A.paniculata was studied. An enhanced rate of andrographolide was found in all the doses of samples using HPLC analysis after gamma irradiation. Gamma irradiation...