SUMMARY— Mullet caught from brackish-water lakes such as Manzala Lake in Egypt were found to serve as an intermediate host for Heterophyes parasite. Infection of man with this parasite may be very heavy. causing severe symptoms. This study revealed that some food-processing methods or treatments may not be adequate to kill the parasite in the fish muscle tissues. It was found that Heterophyes could survive for 30 hr when infected fish were stored at −10 or −20°C. Viability was greater, i.e., 9 days, when stored et refrigerator temperature of 6°C. On the other hand, when fish were dipped in chlortetracycline solution (30 pbm) for 2 hr, the parasite's viability was not affected. Moreover, ice treated with oxytetracycline used for fresh fish preservation had no marked influence on the viability of Heterophyes When infected fish were grilled in a manner quite similar to that adopted by Egyptian fisherman during their fishing trips, about 20-30% of the fish contained living metacercariee of Heterophyes owing to the insufficiency of the heat treatment. Further, in mullet kept at 50 and 100°C, the parasite lived for 180 and 10min. respectively. Thus, insufficient processing or treatment of brackish-water mullet does not completely destroy the parasite, thereby rendering such fish hazardous to the health of persons consuming them.