Securities and Exchange Commission Commissioner Luis Aguilar said Tuesday more stringent regulation of structured notes is needed immediately to protect small investors.

While 99 percent of the purchasers of structured notes are retail investors, Aguilar said, the investments are so complex and the risks are so great that only highly trained financial professionals can understand them.

Structured notes, which come in a variety of flavors, are basically hybrids between bonds and derivatives.

In the prepared text of a speech to the North American Securities Administrators Association in Washington, D.C., Aguilar called upon state regulators and the Financial Industry Regulatory Authority to partner with the SEC in increased oversight of the investment vehicles.

“Nasaa members and Finra have extensive experience with complex products and can provide valuable insights into how these securities are being marketed to retail investors and how to ensure investors are protected,” Aguilar said.

Structured notes first gained notoriety when they helped lead to the downfall of Lehman Brothers and the start of the financial crisis.

The amount of structured notes has increased to $45 billion in 2014 from $38 billion in 2008.