Genzyme's ( GENZ) third-quarter earnings rose 18% from a year ago and beat analysts' forecasts thanks to fattening margins.

The Massachusetts-based biotech earned $115.7 million, or 43 cents a share, in the quarter, compared with $97.8 million, or 41 cents a share, a year ago. Excluding items including amortization, Genzyme's earnings rose 38% to $160.5 million, or 61 cents a share, beating the Thomson First Call consensus by a nickel.

The stock added about 1% to $70.02 early Tuesday.

Revenue rose 24% from a year ago to $708.1 million, about $8 million ahead of forecasts. Sales of Genzyme's biggest drug, Cerezyme for Gaucher disease, rose 14% from a year ago to $238.3 million, while sales of Renagel, a drug for kidney disease, rose 15% from a year ago to $106.9 million in the latest quarter.

Sales of the knee-pain treatment Synvisc more than doubled to $57.7 million after the company acquired sales rights for the drug in the U.S. and five European countries. That performance helped boost Genzyme's overall third-quarter gross margin to 78% from 73%.

Sales of the Fabry disease treatment Fabrazyme rose 36% to $79.1 million, while sales of enzyme replacement Aldurazyme doubled to $20.1 million.