The relationship between Bacillus thuringiensis dose and bollworm, Helicoverpa zea larval mortality, survivorship and movement on and away from cotton leaves was investigated. Bacillus thuringiensis (Costar) was applied to the upper surface of cotton leaves using a spray table in five concentrations i. e., 0.0, 0.14, 0.29, 0.58, and 1.15 kg/ha. Three-day-old H. zea larvae were released on treated leaves, kept at 30 ⁰C, and transferred to artificial diet after 12 h, 24 h, and 48 h. Higher numbers of larvae were found on lower than upper leaf surface at all three transfer times, but the numbers in all treatments were similar to the control. Larval movement from leaf to cup surface was significantly (P < 0.05) higher in B. thuringiensis-treated leaves than the control. Mortality of larvae when transferred from leaves to diet and 7 days after treatment was significantly higher in all treatments than control and highest at the highest rates (0.58 and 1.15 kg/ha). Data on survival of larvae at different locations suggests that at least for the first 24 h, the increase in the percentage of larvae on the inner cup surface in B. thuringiensis treatments was not due to larvae that had consumed a lethal dose, but appeared to be an attempt by larvae to avoid the B. thuringiensis on the upper leaf surface. Highest larval weight was recorded in the control for all transfer times. The length of the larval period increased with dose in the 12-h transfer. Pupal weight reduction was found with the highest doses.