On Memorial Day, the immaculate white shirt comes out of the shopping bag — the emblem and uniform of summer. All too often, though, it's gray, yellow, or dingy by Labor Day.

To determine the best methods for keeping whites white (whether shirts, shorts, napkins, towels, pillowcases, or socks), Real Simple tested dozens of detergents, stain blasters, and whitening agents — from old-fashioned bluing to today's enzyme eaters — and found that it's not so much what you use as how you use it. Contrary to conventional wisdom, chlorine bleach is not the all-purpose answer. The key to maintaining white clothes is frequent laundering, very hot water (the hotter the better), and a little elbow grease. Use the guidelines on the following page and your whites will look right all summer long.

Don't wash whites with colors. Doing extra laundry loads is well worth the effort. "Bleeding from darker colors is one of the main culprits in dinginess," says Lou Protonentis, director for technical services for dyeing and finishing for Cotton Incorporated. Another common cause is detergent residue, which acts as a magnet for dirt. Follow your machine's loading instructions to ensure proper water levels and rinsing.

Use the hottest temperature the fabric can withstand (but always follow a garment's care label). "A 10-degree increase in temperature will increase any detergent's effectiveness," says Jenny Botero, director of housekeeping operations for Marriott Worldwide. Shrinkage can be avoided by drying on low to medium heat.

Inspect garments for stains before laundering. Even if it will be days before the item makes it into the wash, treat a stain with some detergent or a stain product as soon as possible. Allowing a stain to sit will discolor and weaken fabrics.

Wet any stained areas with water before applying a stain blaster. Or use your favorite detergent in the TideKick stain gadget ($1.50 at supermarkets). Its roller-ball applicator releases small amounts of detergent onto stains, leaving them prepped for scrubbing. Work the detergent into a lather by rubbing the fabric together; rinse and repeat until the stain is noticeably lighter or has disappeared.

Remember to inspect garments before drying to ensure that all stains have been removed. "Drying stained garments will bake stains into fibers," cautions Brad Singer, vice president at EISCO, which supplies the cleaning products used to launder the uniforms for most Major League Baseball teams. If stains are still visible after a wash, keep washing until they're gone. Singer also recommends treating stains as soon as possible. He sees to it that baseball uniforms are washed almost immediately after games. "The longer the wait, the harder it is to get stains out," he says.

Resist the impulse to use chlorine bleach to restore whiteness. If you do, make sure to follow the label directions. Bleach breaks down optical brighteners (chemicals with dye that are applied to most white textiles). Over time, bleach leaves clothes yellowed or gray and dingy. "Whiteness will be stripped off a fabric by bleach over time," says Protonentis.

The White Stuff

Biz ($9 for 80 ounces, e-mail biz@redoxbrands.com for store locations) is a color-safe powder bleach that can be used with detergent or on its own as a presoak, Biz noticeably reduced stains and improved overall whiteness.

Shout Ultra Gel ($3, 800-494-4855 for store locations). The scrub-brush applicator on this stain product is great for working up a lather on tough stains. Use it even if you're days away from doing the laundry. It will help keep stains from setting.

Bluette ($12 for 12 pints, 800-338-2329 to order). This bluing agent, which is added to the wash cycle, enhances white (and light-colored) clothes, making them appear brighter and whiter. Bluette won't remove or lighten stains, but it can restore dingy or yellowed whites.