Private equity firm Thomas H. Lee Partners LP acquired a majority stake in Healthcare Staffing Services in a recapitalization transaction. Healthcare Staffing Services specializes in providing nurse staffing on a “rapid response” basis. It owns Fastaff Travel Nursing and U.S. Nursing Corporation.

Healthcare Staffing Services ranks No. 11 on Staffing Industry Analysts’ 2015 list of largest healthcare staffing firms in the US, with $137 million in 2014 US healthcare staffing revenue.

Terms of the transaction were not disclosed. The company will remain at its corporate headquarters in Denver.

“With this investment we will have the scale and resources to accelerate our growth and further expand our platform,” said Ray Marcy, executive chairman of Healthcare Staffing Services. “As we continue to evaluate and pursue new opportunities, both strategic and organic, we are very excited to be partnering with THL — a firm with a long and distinguished track record of helping companies grow and succeed in the healthcare space. As the healthcare industry continues to evolve, HSS’ unique nurse staffing services model is helping hospitals address one of their major issues in ensuring the delivery of quality care — a shortage of well-qualified nurses.”

Thomas H. Lee Partners’ other investments include inVentiv Health Inc., the third-largest clinical/scientific staffing firm in the US.

“We are very excited to be partnering with HSS, a clear market leader in the nursing industry,” said Joshua Nelson, managing director at Thomas H. Lee Partners. “We are looking forward to working closely with Ray and Allison and the talented management team at HSS to further enhance its leadership position and capture this growing opportunity.”

Healthcare Staffing Services acquired Fastaff and U.S. Nursing from Reliant Healthcare in February 2014. Reliant was owned by private equity firm Clarion Capital Partners.