The effects of orchildectomy with/without testosterone replacement in wale rats, and ovarectomy with estrogen replacement in female rats on lipid peroxidation were studied in male and female rats fed with diets fortified with 20% w/w, soybean oil or palm oil for 4 months. Serum, liver and heart homogenates were assayed for malonaldehyde and conjugated diene levels. Orchidectomy was found to reduce levels of lipid peroxidation products in the serum, liver and heart. Testosterone replacement did not increase the lipid peroxidation products to levels in the non-orchildectomised rats, while estrogen did not influence lipid peroxidation significantly. Palm oil decreased, but soybean oil increased lipid peroxidation in the liver and heart of both the castrated and sex hormone-replaced male and female rats.