Imidacloprid (IMI) is a widely used insecticide which has a specific affinity for insect neonicotinoid acetylcholine receptors. Like all insecticides which are used in excess it tends to bioaccumulate in the environment. So it was thought worthwhile to study its cytotoxicity to human peripheral blood lymphocytes in concentrations ranging from 1.5mM to 4mM after 2 hours and 18 hours exposure by MTT method. Trypan blue test was also used to determine the percentage of living cells. The ameliorative effect of an extract of the stem in water and ethanolic extract of leaves of Tinospora cordifolia (Thunb.) Miers, was also studied. The viability of the lymphocytes showed a fall with increasing concentrations at an exposure of 2 hours. After 18 hours exposure to the IMI only, the viability showed a significant dose dependent drop. Trypan blue test for viability was also conducted. Addition of Tinospora extract raised the viability significantly at 2 hours of incubation. In fact this increase was greatest at 3.5mM and 4mM concentration of drug. The ameliorative effect was maximum at 2 hours. Addition of Tinospora leaf extract showed a significant increase in cell viability at 18 hours of incubation as compared to values obtained with only the drug. Thus a considerable loss of viability of lymphocytes was seen after exposure to the drug in the selected concentrations but herbal extracts seem to help to make the damage less marked. The cells showed a significant rise in viability when incubated with Tinospora leaf extract only, confirming its supportive action in cell proliferation. However, taking into account the evident fall in cell viability caused by exposure to the considerably dilute concentrations tested, caution is needed to prevent over exposure to the pesticide while spraying.