Ventana Medical Systems Inc. said on Wednesday that its board unanimously rejected a $3 billion tender offer from Swiss drugmaker Roche Holding AG.

The diagnostics company said in a statement its board determined that the $75 per share offer is inadequate in multiple respects and contrary to the best interests of Ventana's stockholders.

Already one of the world's largest diagnostic companies, Roche announced late last month it would launch a hostile offer for Ventana. The deal represented a 45 percent premium to Ventana shares at the time.

However, Ventana shares have traded above Roche's offer price -- they closed at $80.25 on Tuesday -- indicating investors think a richer proposal could emerge, analysts have said.

Acquiring Ventana, which specializes in tissue-based diagnostics, would give Roche access to technology that helps researchers and doctors better select the right drugs for individual patients.

Roche had said its efforts to negotiate a friendly deal were rebuffed. Ventana on Wednesday took issue with Roche's public statements.

We believe Roche's public disclosures to date are attempts to deliberately mislead the market as to our prior interactions and contacts, Ventana CEO Christopher Gleeson said in a statement.

Ventana said Roche recognizes the attractiveness of Ventana's growth prospects and timed the offer before these factors are fully reflected in the stock price.

In a letter to Roche CEO Franz Humer, which Ventana made public, Gleeson and board chairman Jack Schuler said: We have a serious concern that, to some significant extent, your interest in our company may be based upon confidential information shared with you or your affiliates for collaborative purposes.

Roche was not immediately available for comment. Roche shares were off 0.7 percent.

Gleeson said the Tucson, Arizona-based company remained committed to its business strategy. Ventana plans to provide 2007 and 2008 financial expectations and details about its research pipeline when it releases quarterly earnings later this month.

Roche's bid for Ventana comes amid a spate of deals in the diagnostics sector. Established players are eyeing smaller developers of promising tests and technologies as both an investment in the future of health care and a way to boost cash flow in the near term, analysts have said.

(Reporting by Lewis Krauskopf; additional reporting by Sam Cage in Zurich)