|A solid-object printer was used to produce masters for the fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS). The printer provides an alternative to photolithography for applications where features of > 250 mum are needed. Solid-object printing is capable of delivering objects that have dimensions as large as 250 x 190 x 200 mm. (x, y, z) with feature sizes that can range from 10 cm to 250 mum. The user designs a device in 3-D in a CAD program, and the CAD file is used by the printer to fabricate a master directly without the need for a mask. The printer can produce complex structures, including multilevel features, in one unattended printing. The masters are robust and inexpensive and can be fabricated rapidly. Once a master was obtained, a PDMS replica was fabricated by molding against it and used to fabricate a microfluidic device. The capabilities of this method are demonstrated by fabricating devices that contain multilevel and tall features, devices that cover a large area (similar to150 cm(2)), and devices that contain nonintersecting, crossing channels.