[en] The late-type absorption spectrum of GK Per is classified K2 V-IVp from new spectroscopic observations in agreement with earlier work by Kraft. The fraction of continuum light contributed by the cool component at lambda 4200 is estimated to be about one-third from the depth of the Ca I lambda 4227 absorption line. By combining an effective temperature appropriate to the spectral class with an estimated absolute bolometric magnitude of 5, a radius of 1 to 1.5 R/sub mass/ is found. This is consistent with the photosphere of the cooler component filling its Roche lobe and thus mass exchange is likely to occur. GK Per therefore seems to fulfill at least one of the unusual prerequisites of thermonuclear runaway models for novae as matter is probably accreting onto the primary. The cool component of GK Per, unlike the late-type stars in other cataclysmic binaries, does not appear to be significantly underluminous. (U.S.)