We studied the effects of cooking on the vitamin and mineral content of vegetables (vegetable soup, cauliflower), meat (beefsteak) and fish (sole) and those of cutting (fruit salad) and squeezing (orange juice) on the vitamin content of fruits. In cooked dishes, vitamin retention ranged between 0 (folic acid, all dishes) and 94% (retinol, sole) and mineral retention between 63 (copper, cauliflower) and 96% (iron, vegetable soup). In orange juice, ascorbic acid appeared to be protected from oxidation for at least 12 h as compared with fruit salad. Our study shows that preparation of foods with techniques available at home may be responsible for losses of vitamins and minerals. Further studies are needed to ascertain the effects of these losses on nutritional status.