An early indicator of damage to substantia nigra dopamine neurons in vitro is loss of dendrites that precedes loss of the cell body. To investigate dendritic damage in vivo, rats were treated for 1 day or 1 week with kainic acid (KA; 5 or 10 mg/kg i.p.), the brain fixed and substantia nigra (SN) dopamine neurons and their dendrites labeled using an antibody to tyrosine hydroxylase (TH). KA (10 mg/kg) produced seizures initially and resulted in significant loss of TH immunoreactivity in dendrites of dopamine neurons 1 week, but not 1 day, after a single injection. Daily injections of 5 mg/kg KA, which did not produce seizures, resulted in more extensive dendritic damage. The findings indicate that loss of dendritic staining is a sensitive index of damage to SN dopamine neurons in vivo.