Lysigenous pigment glands scattered throughout the foliar parts of the plant give cotton a degree of insect resistance. These pigment glands contain a complex mixture of terpenoid aldehydes, including gossypol, hemigossypolone, and the heliocides H(1), H(2), H(3), and H(4), which inhibit the growth and development of Heliothis larvae in laboratory feeding experiments. Terpenoid aldehydes have been quantitated in plant tissue by the reaction with aniline. These results are generally reported as "gossypol equivalents" since all of the terpenoid aldehydes react. Thus, the aniline reaction does not indicate the concentration of individual terpenoid aldehydes. We have developed an HPLC method for quantitating each terpenoid aldehyde. Using this technique we have analyzed three cultivars and 11 high gossypol lines of Gossypium hirsutum grown at two locations in Texas. Leaf damage, boll damage and Heliothis larval weights have been correlated with concentrations of individual terpenoid aldehydes. These parameters correlated best with the concentrations of heliocides H(2) and H(3) in the leaves [r = -0.67 to -0.72 and r= 0.63 to -0.66 (P < 0.05), respectively].