  We report here on multifrequency radio observations of the pulsed emission
from PSR B1259-63 around the time of the closest approach to its B2e companion
star. There was a general increase in the pulsar's dispersion measure and
scatter broadening, and a decrease in the flux density towards periastron
although changes in these parameters were seen on timescales as short as
minutes. The pulsed emission disappeared 16 days prior to periastron and
remained undetectable until 16 days after periastron.
  The observations are used to determine the parameters of the wind from the Be
star. We show that a simple model, in which the wind density varies with radius
as r^-2, provides a good fit to the data. The wind is clumpy with size scales
<= 10^10 cm, densities of 10^6 cm^-3 and a velocity of 2000 km/s at a distance
of 20 - 50 stellar radii. We find a correlation between dispersion measure
variations and the pulse scattering times, suggesting that the same electrons
are responsible for both effects.
