A simple evaporative method in sealed capillaries was used to produce X-ray diffraction quality crystals of a monoclonal human Bence-Jones protein (Sea) in microgravity and at unit gravity. The lambda isotypic Bence-Jones protein was purified from the urine of a multiple myeloma patient using ammonium sulfate precipitation, dialysis and cation exchange, followed by gel filtration. Crystals were produced in glass capillaries where water evaporated from the protein solution was absorbed by one or two suitable absorbents. A crystal grown during the 9-day Space Shuttle STS-95 flight measured 8 x 1.6 x 1 mm. It was subjected to X-ray diffraction and was found to be orthorhombic (P2(1)2(1)2(1)). With unit-cell dimensions of 48.9, 85.2 and 114.0 Angstrom. X-ray data were collected at room temperature and were 98.3% complete to 2.3 Angstrom resolution. Crystals of the same Bence-Jones protein measuring 1.2-2 mm in length were grown in ground-based controls using a high evaporation rate for the first 12 h, followed by a slower evaporation rate for the remainder of the 19-day growth period,