A modified capillary-growth method is described that has substantial advantages for standard and high-throughput protein crystal growth. Protein-containing drops are injected into vapor-permeable flexible X-ray-transparent polyester tubing. The protein concentration in the drop increases over time by water transport through the tubing wall at a rate controlled by the wall thickness and ambient relative humidity. Unlike in conventional vapor-diffusion growth, the evaporation rate from the drop is constant over a longer time period, providing more suitable conditions for nucleation, and can be controlled by varying the tubing thickness and surrounding humidity. In situ X-ray diffraction can be performed at room temperature or, by flash-cooling, at low temperatures. Compared with glass capillaries or thick-wall plastic tubing, sealing and handling the tubing and extracting crystals are much easier. © 2005 International Union of Crystallography - all rights reserved.