Technology stocks gave back some of their recent gains amid doubts about the sustainability of one of the strongest rebound rallies on record.

The gains on the Standard & Poor's 500 in the last 50 days are the strongest for any such period on record. Large-cap tech stocks are among the biggest contributors to those gains. The Nasdaq 100 index, which tracks some of the largest tech stocks, fell Thursday after testing an all-time high.

Software maker ZoomInfo Technologies' shares skyrocketed following the company's trading debut Thursday, in what is the biggest technology initial public offering so far this year. Zoominfo, not to be confused with another hot stock, video-conferencing concern Zoom Video Communications, provides database technology to sales and marketing customers. 


 Write to Rob Curran at rob.curran@dowjones.com