The horizontal organization of iso-orientation bands in the cat's visual cortex has been investigated with the 14C-Deoxyglucose method (Sokoloff et al. 1977). Our findings suggest that in areas 17 and 18 the network formed by the bands representing one orientation comprises three basic patterns. Most frequently seen is a set of 2-4 iso-orientation bands which, straight or curved, run parallel to each other through cortical volumes usually less than 3 mm across. Beyond that distance the individual bands either end abruptly or fuse with adjacent bands. Less frequently seen are circular or triangular arrangements, or small isolated patches. Near the 17/18 border the predominant direction of the bands appears to be orthogonal to the vertical meridian, whereas in regions of areas 17 and 18 more distant from the vertical meridian the direction of the bands is more variable. In spite of irregularities in their spatial arrangement, the distance between bands and bandwidth remain constant throughout most parts of areas 17 and 18. The principles underlying the spatial arrangement of iso-orientation bands in the cat's visual cortex have yet to be identified.