Abstract
The regularity or singularity uf data at a point is shown to be preserved for all time at that point along the solution of a pseudoparabolic equation. This significantly strengthens earlier results on the perseverance of global regularity of data and furthermore shows that any local singularities in initial data are stationary, These results yxeld a precise description of the boundary values of a solution and explain certain non-standard maximum principles for pseudoparabolic equations