Order of the Family Court, Kings County, dated May 27, 1966, reversed, on the law, without costs, and a new hearing granted. No questions of fact have been considered. The conduct of the hearing was such that a proper determination on the issue of paternity could not be made. Properly conducted blood test must be given great weight and the trial court should have the proper medical witnesses before it if there is doubt on this issue ( Commissioner of Welfare of N.Y. v. Costonie, 277 App. Div. 90; Anonymous v. Anonymous, 1 A.D.2d 312). The court must also weigh the evidence in the light of a claim of a privilege against self incrimination made by a party on a matter in issue ( Laverne v. Incorporated Vil. of Laurel Hollow, 18 N.Y.2d 635, 638). The court may not substitute appellant's mother in law as the petitioner, but may consider whether to join her as an additional petitioner (CPLR 1002; Family Ct. Act, § 422). Brennan, Acting P.J., Hopkins, Benjamin, Munder and Nolan, JJ., concur.