Order unanimously affirmed, with costs. Memorandum: Lev Zetlin Associates, Inc. (Lev Zetlin), third-party defendant, appeals from Special Term's denial of its cross motion, based on a contractual arbitration agreement between Lev Zetlin and the third-party plaintiff, Paul M. Rudolph, architect, for a stay of the third-party action. Rudolph, defendant in the main action by the City of Niagara Falls for damages due to alleged defects in the city's library building with respect to which Rudolph performed architectural services, commenced a third-party action in June, 1981, against Lev Zetlin, structural engineering consultant to Rudolph on the project. In its answer, Lev Zetlin set forth a cross claim against the other third-party defendant and did not assert its right to arbitration. Subsequently, Lev Zetlin participated in pretrial conferences, examinations before trial, and, to some extent, discovery of expert reports and other documents. It was not until January, 1982, after plaintiff in the main action sought a ruling on the status of the claimed arbitration rights of the third-party defendants, that Lev Zetlin cross-moved for a stay based on its arbitration agreement with Rudolph. We conclude that Lev Zetlin's acts prior to its motion for a stay constitute a "sufficiently affirmative use of the judicial process so as to be inconsistent with a later motion to stay" ( De Sapio v Kohlmeyer, 35 N.Y.2d 402, 406) and that therefore Lev Zetlin has waived its right to arbitration.