Out of various spices and leafy vegetables screened for their influence on the carcinogen-detoxifying enzyme, glutathione-S-transferase (GST) in Swiss mice, cumin seeds, poppy seeds, asafoetida, turmeric, kandathipili, neem flowers, manathakkali leaves, drumstick leaves, basil leaves and ponnakanni leaves increased GST activity by more than 78% in the stomach, liver and oesophagus, - high enough to be considered as protective agents against carcinogenesis. Glutathione levels were also significantly elevated in the three tissues by these plant products. All of them except neem flowers, significantly suppressed (in vivo) the chromosome aberrations (CA) caused by benzo(a)pyrene in mouse bone marrow cells. Multiple CA and exchanges reflecting the severity of damage within a cell were significantly suppressed by these nine plant products. The results suggest that these nine plant products are likely to suppress carcinogenesis and can act as protective agents against cancer.