Titmas

The attorney-client privilege (Evid. Code, § 954), one of the oldest privileges in our jurisprudence, seeks to encourage candid and open discussion. Courts understandably are chary of efforts to turn attorneys against their clients. (But see People v. Gionis (1995) 9 Cal.4th 1196, 1208-1213 [ 40 Cal.Rptr.2d 456 , 892 P.2d 1199 ].) Whether dealing with attorney-client communications or attorney work product, even the liberal principles of discovery are “hardly intended to enable a learned profession to *740 perform its functions ... on wits borrowed from the adversary.” (Hickman v. Taylor (1947) 329 U.S. 495, 516 [ 67 S.Ct. 385, 396 , 91 L.Ed. 451 ] (cone, opn. of Jackson, J.).)

Accordingly, we hold that when there is a prima facie claim of attorney-client privilege, the trial judge must accord a full hearing, with oral argument, before ordering the revelation of client confidences to the other side and, in effect, compelling attorney testimony against a client. The judge in this case (filling in for a vacationing colleague) erred in denying basic due process in this highly sensitive area.

I

Petitioner Ted Titmas invented and patented the Alkohol Stik, a saliva-based…