Protoplasts were prepared from hypocotyls of dark-grown, 8-day-old Chinese cabbage seedlings. Pectinase and cellulase were used together in a one-step procedure. These hypocotyl protoplasts did not contain detectable amounts of chlorophyll. They could be infected in vitro with turnip yellow mosaic virus (TYMV). Virus replication was demonstrated by direct immunofluorescence, enzyme-linked immunosorbent assay, virus recovery by sucrose density gradient centrifugation, and infectivity tests on chinese cabbage plants. The chlorophyll-less hypocotyl protoplasts supported TYMV replication in the dark as well as in the light, while chlorophyll-containing leaf protoplasts allowed TYMV multiplication only in the light.