Rates of infestation by the pink and spiny bollworms, in cotton squares, flowers and green bolls, were studied in Giza region, throughout July—September, 1974 and 1975. In the first season, infestation by Pectinophora gossypiella was almost dominant on the three sites, as rate of infestation increased gradually from July (1–12%) to September (33–92.3%), but infestation in bolls was much higher than on the other two sites. In the second season (1975), Earias insulana took a good share in infestation together with Pectinophora gossypiella, especially on cotton squares and flowers, at the end of the season, whereas P. gossypiella was more dominant on green bolls, reaching in September 70–80%, as compared to 16–34% for E. insulana. Linear regressions were calculated, and proved significant in most cases, for the relationship with time (from 1st July till end of September) of the rates of infestation and number of larvae of P. gossypiella and E. insulana in both seasons, at various sites of infestation. Number of different instar larvae of P. gossypiella at the three sites of infestation, were recorded in the two seasons. Generally, first instar larvae were more dominant on squares, whereas older (2nd–4th instar) larvae were more frequent on flowers and green bolls. At the end of two cotton seasons (October 1973 and 1974), percentages of sound (pickable, fully opened) bolls were 29.8–53.5%, those of partially opened bolls were 27.6–41.9% and those of closed bolls (fully damaged) were 18.9–28.2%. Thus, from 47–70% of the cotton bolls were damaged by bollworms, mostly P. gossypiella.