Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) are major pests of cotton in Australia. The density of eggs and larvae of these species are sampled regularly throughout the growing season to assess the need for insecticidal control. A sampling system now widely used is based on binomial sampling combined with a series of conversion relationships developed as part of the SIRATAC computer based pest management system established in the early 1980s. A three year study was initiated to reassess the binomial sampling conversion relationship in the light of changed agronomic practices and new cotton varieties. New relationships were established to predict the mean number of Helicoverpa spp. present, based upon the number of infested plants found within a sample. Relationships are reported for the sampling of whole plants and the sampling of the terminal (top 20 cm) portion of cotton plants only. These new relationships will be incorporated into entomoLOGIC, a personal computer based pest management system now released to replace SIRATAC.