The hyperoxaluric rat kidney nucleus exhibited a 50% increase in oxalate binding activity of control in both the residual fraction containing nuclear envelopes and the histone fraction with a concomitant increase in basal lipid peroxidation and a decrease in thiol content. However, in vitro lipid peroxidation induced by the ascorbate-ADP-Fe3+ system increased the oxalate binding activity of the residual fraction with a positive correlation but inhibited the histone oxalate binding activity with a negative correlation with depletion of thiols during peroxidation in both control and hyperoxaluric rats. A twofold increase in oxalate concentration was observed in the nucleus as well as the nuclear subfractions in hyperoxaluria. Hyperoxaluric rat kidneys showed increased H1 and oxalate binding activity, and the distribution of H1B was higher than that in the control. The present study suggests that the increased nuclear oxalate binding activity in hyperoxaluric rats was not due to lipid peroxidation but due to increased formation of histone H1. © 1997 S. Karger AG, Basel.