Place a steamer over a pot of boiling water. Cut Swiss chard crosswise into 3/4-inch pieces, keeping greens and stems separate. Place stems in steamer, and steam for 5 minutes. Add greens, and steam for 3 minutes more. Drain well.
In a large saute pan, heat butter over medium-low heat. Add Swiss chard, and toss until well coated with the butter. Season with salt and pepper. Serve immediately.