The paper examines the preverbal markers in Mengrelian as the possible loci of post-syntactic phonological rules that affect the allomorphy of these preverbs. The goal of the paper is to pinpoint the series of these rules and the extent to which the final form of the derived material changes as a result of their application. The phonological rules are examined in light of cyclic and post-cyclic processes that have different local domains of application such as nested constituents for the former and entire words for the latter (Halle & Nevins, 2009). It is shown that that phonological rules may obscure the derivation of surface forms from underlying representations and that the meaning of preverbal markers may not be kept as a result of  these changes. The paper concludes that the derivational view of morphology such as Distributed Morphology (Halle & Marantz, 1993) should be modified to accommodate these data. Keywords: cyclic, post-cyclic, phonological rule, preverb, PF