Preliminary experiments dealing with the assimilation of significant wave heights (SWH) from the Seasat altimeter into the National Oceanic and Atmospheric Administration Ocean Wave (NOW) global spectral model are discussed. For all experiments, National Meteorological Center--analyzed winds for the Seasat period were used to drive the ocean surface. A hindcast was first made running the model with no assimilation for use as a control. The model was then run, using both simple replacement and a blending procedure to spread the influence of an observation to nearby grid points and for different assimilation frequencies. Forecasts of SWH from each assimilation run and the hindcasts are compared to the corresponding Seasat SWH estimate from subsequent satellite passes. Best results are obtained by using a 3-hour assimilation frequency with simple replacement and by scaling the forecasted spectrum with the observed SWH. A mean improvement of 7.7% (¿8.4% at the 90% confidence level) is thus achieved for the 10 days of the experiment, with a maximum improvement of 25%.