Ribonuclease (RNase) activity of tomato leaflets increased 3–6 hours after excision in air and then declined to attached leaf levels within 12 hours after excision. Leaflets submerged in a c bar mannitol solution during excision failed to exhibit a significant RNase ‘pulse’ while more dilute mannitol solutions and a dilute nutrient solution failed to suppress this increase in RNase activity; the RNase ‘pulse’ appears to be a response to a disrupted water balance in the leaflet. The RNase response to leaf excision was also reduced by immersing air-detached leaflets in 0.2 ppm indoleacetic acid (IAA). Kinetin solutions were effective at 2 ppm when leaflets were immersed in kinetin solutions for 4 hours before excision as well as after detachment. Kinetin and IAA also suppressed gradual increases in RNase activity characteristic of tomato leaflet senescence. IAA and kinetin together were somewhat less effective than IAA applied alone. Cytidylic and adenylic acids as well as chloramphenicol were also effective in inhibiting this long term increase in RNase activity.