As part of a study of the behavior of wood joist floors at various limit states, an attempt was made to estimate the slip between joists and plywood at selected locations on 12 full-scale test floors. Results are reported in terms of measured slip values and the resulting nail forces estimated from a nail force-slip relationship. These forces were generally found to be less than the published allowable values for nails in single shear when the applied floor load was 40 lb./ft.². Measured slip values at floor loads of 40 lb./ft. ² were also found to be less than the commonly accepted value for the proportional limit slip. Finally, it was determined that joist stiffness cannot be used to predict the location of the greatest magnitudes of slip. -- AATA