YSI & SonTek Announce Acquisition of
San Diego-Based SonTek by YSI

Yellow Springs, Ohio & San Diego, California, July 9, 2001 - YSI Incorporated of Yellow Springs, Ohio, and SonTek, Inc. of San Diego, California, announced today that YSI acquired the assets of SonTek and formed a new company, SonTek/YSI, that will operate as a wholly-owned subsidiary of YSI Incorporated. The synergistic relationship between SonTek and YSI will greatly enhance water testing, water monitoring, and water velocity measurements.

SonTek, founded in 1992 with the goal of producing high-quality Doppler current meters, will be part of YSI Environmental, headed by Gayle Rominger, Sr. Vice President and General Manager. YSI Environmental has a worldwide reputation as a leader in the measurement and monitoring of water quality parameters, particularly dissolved oxygen, which is necessary for the survival of plant and animal life in water. SonTek is considered the world leader for water velocity measurement.

"With this acquisition we now have a powerful and strategic combination of capabilities in both water quality and water quantity," says Malte vonMatthiessen, YSI Chairperson and CEO. "Both our companies have achieved significant prominence in our respective marketplaces. We have combined the two fastest growing companies in the water quality and water velocity markets." He adds that, "The natural resources market presents a worldwide opportunity, and YSI and SonTek, together, have the ability to revolutionize this global market."

According to SonTek CEO Ramon Cabrera, "Not only can YSI and SonTek collaborate in the area of sales and distribution, but there are exciting opportunities for joint product research and development." Mr. vonMatthiessen expresses his delight at Cabrera's willingness to stay on with SonTek/YSI and states that "Ramon is vital to the continued success of this business, and we are fortunate that he has agreed to continue to lend his technical and market expertise--as well as his vision--to this newly-formed enterprise." Mr. Cabrera notes, "SonTek's ability to integrate water quality sensors with our acoustic Doppler technology will allow us to respond to a new and very important need in the marketplace."

SonTek manufactures affordable, reliable acoustic Doppler current profilers, velocimeters, Doppler velocity logs, and integrated systems for use in oceans, rivers, lakes, harbors, estuaries, and laboratories. YSI Environmental, a wholly-owned subsidiary of YSI Incorporated, manufactures a full line of both handheld and bench-top instruments for measuring water quality. It also manufactures data acquisition and multi-parameter, real-time monitoring systems for environmental applications (see www.YSI.com).

YSI Incorporated is an international company with world headquarters based in Ohio. The employee-owned company manufactures and markets sensor technologies dedicated to ecological sustainability. Its three strategic business units include YSI Environmental, YSI Precision Temperature, and YSI Life Sciences.