Updated from 5:23 p.m. EST

Tyco ( TYC) continued to climb in after-hours trading, building on the momentum the stock picked up late in the day after Standard & Poor's expressed confidence in the company's accounting and two executives said they would buy back stock.

The conglomerate's shares were down for much of the regular session, but Tyco rebounded to close up 3.3%. In extended action, the stock was gaining 1.9% to $35.50.

Polymedica ( PLMD) was dropping 5.6% to $18.50, making the stock one of the late session's biggest losers, after the company forecast revenue of $73.5 million to $74.5 million in the fourth quarter and $278 million to $279 million for the fiscal year. The stock was the most actively traded on Instinet after the bell.

Affymetrix ( AFFX) was dropping 3.7% to $30.20 after the company posted fourth-quarter earnings, excluding items, of a penny a share. Analysts were looking for a loss of 5 cents. Including items, Affymetrix lost 15 cents. For 2002, the company expects earnings, before items, of $3 million to $5 million.

As usual, widely held tech issues were taking up plenty of space on the most-actives list. Intel ( INTC) was inching up 0.1% to $33.90. AOL Time Warner ( AOL) was ticking up 0.2% to $26.46.

VeriSign ( VRSN) was flat at $31.76, and Cisco ( CSCO) was up 0.3% at $19.39. Sun Micro ( SUNW) was adding 1% to $10.98, and WorldCom ( WCOM) shed another 1.2% to $9.73.

Oracle ( ORCL) was up 0.7% to $16.74, and Microsoft ( MSFT) was off 0.1% at $62.81. The Nasdaq 100 Tracking Stock ( QQQ) was tacking on 0.3% to $38.38.