The Conference Board says its index of leading indicators increased 0.1 percent last month to a reading of 95.2. That followed a stronger 0.8 percent rise in April.
Higher stock prices boosted the May index.
The index is intended to signal economic conditions three to six months out. It has been posting steady gains since December, one of many favorable signs for a stronger second half of the year.
Conference Board economist Ken Goldstein said growth will depend on the strength of housing and consumers, which have helped offset government spending cuts and weak exports.