We have used the resonance radiation pressure from 40 mW of cw dye laser light propagating axially down a tube filled with sodium vapor to increase the sodium pressure (density) up to 50% over a length of 20 cm. The magnitude of the effect agrees well with measurements of the absorbed power. These observations were made with the laser tuned to the low‐frequency side of the sodiumD2resonance line; for tuning to the high‐frequency side, an additional unexplained effect leading to density decreases was observed.