The Westerbork Telescope has good low-frequency capability, with receivers covering much of the frequency range from 250 to 1800 MHz. For pulsar observations the array elements can be coherently summed to provide the equivalent of a 93 m aperture. To exploit this potential, a new backend, PuMa, has recently been commissioned. It can be configured in various ways, with up to 4096 frequency channels per band, a total bandwidth of 80 MHz, and time resolution of 50 nanoseconds. PuMa can be used in search mode, recording just two polarization channels, or for observations of known pulsars, determining all four Stokes parameters and correcting for dispersion and Faraday rotation. In many of the low-frequency bands (especially 300 — 380 and 800 — 900 MHz) interference-free observing is possible much of the time, enabling wide-band studies of ISS, refraction and the Faraday effect.