To the Editor: A Brief Recording by Nachnani et al., "Scanning Electron Microscopy of Thrombogenesis on Vascular Catheter Surfaces" (Vol. 286, p. 139) has reverberated extendedly among angiographers and commercial representatives and in the literature, with a demonstrably false message — namely, that polyurethane (Poly U) catheters are rough whereas polyethylene (Poly E) catheters are smooth, and that, as an implicit corollary, Poly U catheters predispose to excessive thrombogenesis.Our experience with the use of Poly U catheters both in the laboratory and in more than 10,000 clinical examinations has been precisely the opposite. Not wishing to be the last . . .