Analyses of hydrographic data from a single winter cruise and of 29 years of climatological surface temperature data are used to describe some horizontal and vertical properties (and their interrelations) of a large-scale longitudinal temperature maximum in the eastern North Pacific. The climatological surface temperature data for individual monthly means at 35¿ and 40¿N from 1947 to 1975 show that (1) the position of the permanent large-scale tempeature maximum at 35¿N in the eastern Pacific almost always lies in the west of that of the corresponding maximum at 40¿N, and the average angle counterclockwise from the east of the line connecting the two maxima is about 40¿ and (2) a positive correlation exists between the temperature and east-west scales of the longitudinal temperature variation at 40¿N. Both results agree with preliminary analyses based on long-term averages of monthly mean temperatures (Kenyon, 1977a). The hydrograhic data from March and April 1976 along 35¿N show that both the depth scale and the east-west scale associated with the temperature maximum in the eastern Pacific can be related to the surface layer thickness and are about 100 m and 4000 km, respectively. The surface layer thickness, defined by a temperature-salinity relation, is relatively large (small) when the surface temperature is relatively high (low), a relation which holds for the large-scale horizontal variability in the eastern Pacific as well as for the smaller-scale (500 km) variability in the western Pacific. The hydrographic data at 35¿N show also that the maximum surface temperature in the eastern Pacific is significantly west of the maximum surface layer thickness. Beneath the maximum surface layer temperature, where the vertical temperature gradient is large, the isotherms slope downward from west to east. The geostrophic surface velocity relative to 250dbar, where the isotherms are nearly level, has a northward component in a broad region surrounding the surface temperature maximum. The hydrographic data strengthen the interpretation that the longitudinal surface temperature maximum is predominantly associated with horizontal advection in the surface layer, which has a significant northward component, and is the surface expression of a mechanism of net poleward heat transport in the eastern Pacific.