From CHOW.com
1 bunch red radishes (about 13 radishes)
1/2 cup red wine vinegar
1/4 cup granulated sugar
1/4 cup water
2 teaspoons kosher salt
1/2 teaspoon yellow or brown mustard seed
1/4 teaspoon whole coriander seed
1/4 teaspoon whole black peppercorns
1 medium dried bay leaf
1) Thinly slice radishes, put in a glass bowl in the refrigerator,
discard the tops.
2) Combine red wine vinegar, sugar, water, salt, mustard
seed, coriander seed, peppercorns, and bay leaf in a small
saucepan and bring to a simmer over medium-high heat.
Stir occasionally until sugar is dissolved.
3) Remove from heat and let pickling brine cool for about 5
minutes. Remove radishes from the refrigerator and pour
brine over them. Let cool at room temperature for 20 minutes;
cover and refrigerate.