Georgian, a South Caucasian language belonging to the Kartvelian family, is characterised by the ability of its consonants to combine in extensive clusters. Among the possible combinations are a series of two-member clusters which are argued to behave phonologically as single segments (Tschenkeli 1958, Vogt 1958, 1971, Aronson 1982, 1991, Deprez 1988 and others). They are known as ‘harmonic’ clusters, because the laryngeal quality is constant across the cluster. Its two members are both voiced ([dg bg dγ bγ]), both aspirated ([thkh tshkh thχ tshχ]) or both ejective ([t'k' ts'k' p'k' t'q' ts'q']). They can occur either word-initially or in word-medial position. Harmonic clusters do not contrast with identical sequences of segments, except for sequences formed at the junction of two words. There is no evidence that across word boundaries harmonic clusters are derived by some sort of restructuring. The purpose of the present study is to review the phonological arguments brought in the literature in favour of treating harmonic clusters as single segments, and to look for acoustic evidence that would motivate the distinction made between harmonic clusters behaving as single segments, on the one hand, and simple sequences of consonants, on the other hand. The study uses phonetic data to address the issue of phonological representation. If the difference between a harmonic cluster and a simple sequence of segments is present in the phonology, then it should ideally also be visible in the acoustic signal, for example in the presence or absence of a release burst, or in timing differences, as suggested by previous studies of complex vs. simple segments in various languages (Maddieson & Ladefoged 1989, Maddieson 1989, 1990). The results show that the treatment of Georgian harmonic clusters as complex segments is not supported by the acoustic data. The paper is organised as follows: § 2 presents the phonological behaviour of consonant clusters in Georgian, § 3 reviews phonetic evidence for complex segments, and spells out the predictions made by the present study. The acoustic study is described in § 4, followed by the presentation and discussion of results in § 5. The conclusions and areas for further study are presented in § 6.