The present invention relates to ethynyl compounds of formula wherein X, Y, Z, and R4 are as defined herein or to a pharmaceutically acceptable salt or acid addition salt, to a racemic mixture, or to its corresponding enantiomer and/or optical isomer and/or stereoisomer thereof. Compounds of formula I are positive allosteric modulators (PAM) of the metabotropic glutamate receptor subtype 5 (mGluR5) and they are therefore useful for the treatment of diseases related to this receptor.
