An important aspect of Integrated Pest management (IPM) is to use biocontrol as a strong component if not the underlying basis for IPM programs. A major problem is the use of biocontrol and chemical control in the same program. Entomopathogens provide biocontrol possibilities that may be compatible with conventional pesticides. In 1993 and 1994, we used the entomopathogenic fungus, Beauveria bassiana as Naturalis-L^® for control of silverleaf whitefly in cotton. In this study, we present work with Paecilomyces fumosoroseus (PFR-97^®) and additional work with the fungus B. bassiana, (Naturalis-L^®and Mycotrol^®WP). Our objective was to determine if these fungi can be used successfully to control SLWF in the arid southwestern US and hence be biocontrol components in an IPM program. Endosulfan (Phaser^® 3EC and Gowan Endosulfan 50WSB) was used as a tank-mix component in some treatments; in those treatments each product was used at half rate. The study was done with Deltapine 5415 cotton. The fungi/insecticide treatments were part of a 16-treatment random block design that included a "best agricultural practice regime", a water-treated control; and nearby was a separate untreated, 1-ac solid-planted, unsprayed, block control. Treatments were replicated 4 times in a random block design. Eggs, small nymphs, and large nymphs were sampled from the fifth main-stem leaf down from the first expanded terminal leaf and reported as mean no./cm². Adults were sampled from 30 leave/plot /week, and sweep samples were taken in all plots for predators, parasites, and Lygus. Applications were made by ground and sprays were applied at 80 psi and 30 gal./ac. Data are presented as plots of treatments and as efficacies as % reduction from sample means of the untreated control block.