The changes in DA-D2 receptor mRNA expression following apomorphine induced hypothermia and stereotypy were determined. Rectal temperatures and stereotypy were measured daily after apomorphine injection to Sprague-Dawley rats for 7 days. DA-D2 mRNA expression was determined by Northern blot analysis. Apomorphine caused a dose dependent decrease and increase in rectal temperatures and stereotypy respectively. Northern blot analysis indicated a relative abundance of the DA-D2 receptor message at the high and a reduction at the lower dose of apomorphine. The result showed that the agonist activity could influence the expression of DA-D2 receptor mRNA.