KLA-Tencor (KLAC) had the lowest return in March 1989 by a US stock in the S&P 500 (GSPC), returning -20.4%.

ASSET	MONTH	% RETURN
KLA-Tencor (KLAC)	March 1989	-20.37%
Lam Research (LRCX)	March 1989	-18.8%
Microsoft (MSFT)	March 1989	-15.81%
Best Buy (BBY)	March 1989	-13.79%
Analog Devices (ADI)	March 1989	-13.68%
Constellation Brands Inc Class A (STZ)	March 1989	-12.5%
FedEx (FDX)	March 1989	-10.86%
International Business Machines (IBM)	March 1989	-10.64%
MGM Resorts International (MGM)	March 1989	-9.78%
Pentair (PNR)	March 1989	-7.94%
Teradyne (TER)	March 1989	-7.92%
CSX (CSX)	March 1989	-7.34%
Bio-Techne (TECH)	March 1989	-6.89%
HP (HPQ)	March 1989	-6.87%
Newmont Goldcorp (NEM)	March 1989	-6.47%
Western Digital (WDC)	March 1989	-6.06%
Pinnacle West Capital (PNW)	March 1989	-5.78%
Ford Motor (F)	March 1989	-5.78%
Monster Beverage (MNST)	March 1989	-5.59%
Becton Dickinson and (BDX)	March 1989	-4.94%
McKesson (MCK)	March 1989	-4.76%
Tyson Foods (TSN)	March 1989	-4.76%
JB Hunt Transport Services (JBHT)	March 1989	-4.55%
Williams Companies (WMB)	March 1989	-4.36%
Air Products and Chemicals (APD)	March 1989	-4.3%