Pelton ladder on the Deschutes River was used to estimate migration tendency in juvenile spring chinook salmon. A positive relationship between elevated levels of gill (Na+K)‐adenosine triphosphatase (ATPase) and migration tendency was determined in 1977 and 1978. Migrant fish had significantly higher ATPase activities than nonmigrants. In 1978, a distinctive peak in (Na+K)‐ATPase was observed in hatchery‐reared fish, while this peak was absent in 1977. This suggests caution in the use of gill (Na+K)‐ATPase as an indicator of smolting for hatcheries.