Biotechnology has surged higher in recent months as a combination of good news and speculation lifted the group's well-knowns and unknowns alike, but on a day that sellers took control of the broad market, this superheated sector also took a tumble.

Two broad sector measures reflected the selloff. The Amex Biotech Index ended the day down 4.6%, and the Nasdaq Biotech Index gave up 6.1%.

Individual stocks were hit hard, and one of those feeling the pain most acutely was Protein Design Labs ( PDLI), which fell nearly 11% to $15.35. Human Genome Sciences ( HGSI) dropped almost 8% to $12.40. Vertex ( VRTX) lost 6% to $14.62.

Elsewhere in sector, Genzyme ( GENZ) fell 6% to $43.48, Millennium ( MLNM) shed almost 6% to $14.96, and Chiron ( CHIR) was down 5% to $44.75.

Most of the well-known names in the group were under some degree of selling pressure, including Biogen ( BGEN), off 5% to $43.25, and Amgen ( AMGN), lower by 3% to $63.82. Genentech ( DNA) held up relatively well, declining only 0.6%, or 46 cents, to $74.07. Helping support Genentech was a bullish report from research firm UBS on the stock and the company's prospective cancer treatment Avastin.

Gilead ( GILD) was off 5% to $51.30, and MedImmune ( MEDI) declined 1% to $35.76.

(Adam Feuerstein, a columnist for TheStreet.com's sister site RealMoney.com, took a look today at the biotech sector's recent run-up, and he offered some insight regarding just how long the optimism might continue lifting these stocks.)

The smaller-cap names were also seeing their fair share of selling. Oxigene ( OXGN) was down 11% to $9.01. Geron ( GERN) lost more than 4% to $6.86, while VaxGen ( VXGN) slipped 2% to $5.06.

Large pharmaceutical companies headed lower, as well. Novartis ( NVS) was down 0.6% to $41.60, Pfizer ( PFE) dropped 1.3% to $35.60, and Merck ( MRK) lost 1.5% to $62.30. Meanwhile, GlaxoSmithKline ( GSK) fell 3% to $41.70.

Forest Laboratories ( FRX) was sent down 12% to $53.29 after the company reported disappointing data from a recent study involving the company's Alzheimer's treatment. The Amex Pharmaceutical Index declined 2% on the day.