The effects of omega 3 fatty acids and epidermal growth factor (EGF) on the activity of receptor tyrosine kinase (RTK) and phospholipase C (phosphatidylinositol (PI)-specific PLC) were examined in EMT6 cells. The non-omega 3 treated, non-EGF stimulated cells served as controls. Treatment of the EMT6 cells with omega 3 fatty acids resulted in a 62% increase in RTK activity and a 67% increase in PI-specific PLC activity. When EGF was added to incubations for RTK activity, it stimulated the RTK activity 40% in the control cells and 130% in the omega 3-treated cells. When EGF was added to incubations for PI-specific PLC activity, a 54% increase in PI-specific PLC activity was observed in control cells and a 94% increase in the omega 3-treated cells. Thus, treating EMT6 cells with omega 3 fatty acids seems to increase RTK activity and PI-specific PLC activity to a similar extent, but has differential effects on the ability of these enzyme activities to be stimulated by EGF.