Merck (MRK) had the highest return in October 2000 by a mega-cap US stock, returning 21%.

ASSET	MONTH	% RETURN
Merck (MRK)	October 2000	21.03%
Intuitive Surgical (ISRG)	October 2000	15.95%
Microsoft (MSFT)	October 2000	13.84%
Caterpillar (CAT)	October 2000	13.11%
Thermo Fisher Scientific (TMO)	October 2000	11.54%
Abbott Laboratories (ABT)	October 2000	10.6%
UnitedHealth (UNH)	October 2000	10.48%
Eli Lilly and (LLY)	October 2000	10%
Taiwan Semiconductor Manufacturing (TSM)	October 2000	9.34%
Coca-Cola (KO)	October 2000	9.28%
Costco Wholesale (COST)	October 2000	9.12%
Procter & Gamble (PG)	October 2000	7.03%
Royal Bank of Canada (RY)	October 2000	6.62%
Berkshire Hathaway (BRK.B)	October 2000	2.59%
McDonald’s (MCD)	October 2000	1.85%
Raytheon Technologies (RTX)	October 2000	1.36%
HSBC Holdings PLC ADR (HSBC)	October 2000	1.26%
Wells Fargo (WFC)	October 2000	0.68%
Toyota Motor Corporation ADR (TM)	October 2000	0.41%
Exxon Mobil (XOM)	October 2000	-0.21%
Berkshire Hathaway (BRK.A)	October 2000	-0.47%
Novartis AG ADR (NVS)	October 2000	-0.81%
American Express (AXP)	October 2000	-1.51%
LIN TV (LIN)	October 2000	-1.65%
JPMorgan Chase (JPM)	October 2000	-1.74%

Mega-cap stocks are treated as having a market cap of $200B+.