Shares of COR Therapeutics ( CORR) were under severe pressure, falling 13.3%, to $17.85, after the company issued a profit warning just before the closing bell. COR, a developer of treatments for heart disease, said it expects to earn a penny a share in the third quarter, well below the 8 cents expected by Wall Street. The company blamed lower-than-expected sales from its Integrilin drug. The stock was the second largest volume mover on Instinet.

Overall volume on the ECN was extremely heavy as more than 7.5 million shares changed hands in the first 40 minutes of trading, with 3.3 million shares moving among the Instinet top 20 volume movers.

Polycom ( PLCM), a videoconferencing provider, was among the early volume leaders as it dropped 1.4%, to $29.90. Earlier in the day Polycom and PictureTel ( PCTL) said they agreed to modify terms of their merger agreement. Polycom said it will waive a clause that relates to a "national calamity" or "armed hostility involving the U.S." which could have kicked in after the terrorist attacks.

Quest Software ( QSFT) was another big loser, dropping 5.3%, to $15. The company said it expects pro forma earnings of a penny to 2 cents a share, well short of the 6 cents analysts were looking for. The company also added 3 million shares to an existing buyback program.

Research In Motion ( RIMM) was up 8.3%, to $17.10. The company said it earned 5 cents a share before various items in the second quarter; analysts were predicting 4 cents a share. The company's revenues nearly doubled from a year ago to $80.1 million.

Overall on Instinet, the Nasdaq 100 tracking stock, or QQQ, was the leading volume mover, slipping 0.1%, to $30.96. Among other perennial after-hour names, most were little changed from the close. Cisco ( CSCO) was up 0.1%, to $13.96, while Dell ( DELL) gained 0.2%, to $20.69. Sun Microsystems ( SUNW) fell 0.1%, to $8.99, and Intel ( INTC) remained unchanged at $21.23. Veritas Software ( VRTS) was up 1.1%, to $23.75.

10 most active stocks on Island ECN (4:40 p.m. EDT)
Company Price Change Session Volume
Nasdaq 100 Tracking Stock (QQQ) 31 0.00 573,685
Cisco Systems (CSCO) 13.97 +0.02 143,360
Research In Motion (RIMM) 17.60 +1.81 138,082
Check Point Software Technologies (CHKP) 26.28 +0.29 57,829
Sun Microsystems (SUNW) 9.04 +0.04 57,526
Openwave Systems (OPWV) 6.54 -0.10 45,875
Ion Networks (IONN) 0.12 -0.01 44,495
JDS Uniphase (JDSU) 7.10 -0.03 41,672
Andrx Corp. (ADRX) 74.69 -0.24 36,402
Juniper Networks (JNPR) 11.95 -0.05 33,783

Island ECN offers trading, mainly in Nasdaq-listed stocks, from 7 a.m. to 8 p.m. EST.

Confused? TheStreet.com explains how the rules change when the sun goes down in Investing Basics: Night Owl, a section devoted to after-hours trading.

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