Updated from 2:53 p.m. EDT

Shares of

Able Laboratories

( ABRX) were easily among the worst-performing health-related stocks Thursday, falling 74.6% on huge volume after the company said it would halt the shipment of all of its products because of improper laboratory practices. The company also announced the resignation of its chief executive.

Able said it recently recalled some of its products, although it didn't specify which, after finding problems with its manufacturing and testing procedures. The company's generic portfolio is large, encompassing painkillers, blood-pressure treatments, antibiotics and other drugs. With nothing shipping, the company withdrew its old financial guidance.

After the company's business-practice disclosures, Able announced the resignation of its chief executive officer. The company said that Dhananjay Wadekar would be replaced by Robert Mauro, who will serve as interim CEO. Wadekar will continue to work with the company as a consultant. Shares traded down $18.37 to $6.26 on volume of 31 million shares, or almost 127 times its normal daily average.

Mentor

( MNT) rose 2.2% after the company posted fourth-quarter results that topped forecasts. The maker of health care products earned $8.4 million, or 19 cents a share, on sales of $131.6 million. Excluding items, the company would have earned 42 cents a share. Analysts polled by Thomson First Call were expecting earnings of 37 cents a share on sales of $128.9 million. A year ago the company earned $15 million, or 31 cents a share, on sales of $117.3 million.

Looking ahead, Mentor forecast fiscal 2006 earnings of $1.60 to $1.65 a share on sales growth that is expected to be in the low double digits. Analysts are expecting earnings of $1.56 a share on sales of $537.6 million. Shares traded up 86 cents to $40.56.

OccuLogix

(RHEO)

, a health care company focused on eye-care treatments, announced Thursday that John Caloz will succeed William Dumencu as chief financial officer and treasurer. The appointment is effective June 1. Dumencu will remain with the company and serve as vice president of finance. Caloz most recently served as CFO for medical device maker

IRIS International

( IRIS). Shares traded down 16 cents to $8.45.

Other health-care volume movers included

Pfizer

(PFE) - Get Report

, up 28 cents to $28.72;

Cyberonics

(CYBX)

TST Recommends

, down $4.69 to $34.18;

Amgen

(AMGN) - Get Report

, down 53 cents to $61.82;

Merck

(MRK) - Get Report

, down 16 cents to $32.79;

Elan

(ELN)

, down 6 cents to $7.30;

Johnson & Johnson

(JNJ) - Get Report

, down 19 cents to $67.41;

Schering-Plough

( SGP), down 20 cents to $20;

Bristol-Myers Squibb

(BMY) - Get Report

, up 6 cents to $25.45; and

Genentech

( DNA), up $1.15 to $75.15.