Appeal by defendant from a judgment of the County Court, Dutchess County (Rosenblatt, J.), rendered May 2, 1977, convicting him of criminal sale of a controlled substance in the third degree (two counts) and criminal possession of a controlled substance in the third degree (two counts), upon a jury verdict, and imposing sentence. Judgment affirmed. On this appeal defendant argues: (1) that the known substance relied on for comparative tests was not established as reliable by either of the testifying experts and (2) that comment in the prosecutor’s summation on the failure of defendant or witnesses on his behalf to contradict the testimony of the police officer deprived him of a fair trial. As to the reliability of the known substance as a compara*583tive standard, the record does not disclose an objection to the admissibility of the expert testimony which would have directed the trial court’s attention to the specific ground as now alleged in the defendant’s brief. Hence, the alleged error is not preserved for appellate review (CPL 470.05, subd 2). Likewise with respect to the prosecutor’s remarks in summation the record contains neither objection thereto nor request for a curative instruction. (People v Medina, 53 NY2d 951.) In any event, the evidence of guilt was overwhelming and such errors were not so prejudicial “as to suggest that the jury would have reached a different result in their absence (People v Crimmins, 36 NY2d 230)” (People v Woolley, 53 AD2d 779). Mollen, P.J., Hopkins, Titone and Weinstein, JJ., concur.