Although narrow row spacings in cotton Theoretically increase total seasonal light energy interception, this increase does not consistently translate into greater dry matter accumulation or higher lint yields. In a 1989 field study, cotton (Gossypium hirsutum L.) was grown in rows spaced both 0.5 m (narrow) and 1.0 m (wide) apart. Two genotypes, an Okra leaf-and normal leaftype were grown. An early season (mid April) and a late season (late May) planting dates were used. Light penetration through the canopy, solar insolation interception, dry matter accumulation, and leaf area were determined throughout the season. Lint yield and lint percent were determined at maturity. Narrow row spacing increased solar insolation interception in both leaftypes and for both planting dates. The narrow row spacing increased lint yield of the okra leaftype by 22 and 34% in the early and late season plantings, respectively. However, lint yields of the normal leaftypes were not affected by row spacing. Lint yields were not significantly different between leaftypes. The higher lint yield of narrow row okra leaftype over wide row spacing was associated with a 27% increase in the number of bolls per unit area. Narrow rows increased the efficiency by which a given leaf area intercepted light. In narrow rows, a leaf area index (LAI) of 3 intercepted 87% of incoming insolation but in wide rows an LAI of 3 resulted in only 76% interception. Despite differences in solar insolation interception and lint yield between row spacings, differences in crop growth rate, harvest index, or lint percent between row spacings were not detected. Narrow row spacing appeared to increase yield only for Okra leaftypes which are not routinely grown commercially.