Cowpea mild mottle virus (CMMV) has physicochemical properties typical of carlaviruses, but has remained unclassified due to a number of unusual properties, including no serological cross-reaction with l 8 carlaviruses; production of brush-like inclusion bodies in vivo; and the ability to be transmitted by whiteflies (Bermisia tabaci).In this paper we report the use of a carlavirus specific PCR primer to identify CMMV as a member of the carlavirus group. This is confirmed by nucleotide sequence (958 nucleotides) from the 3' terminal region of CMMV RNA which contains a partial open reading frame (ORF) having high similarity with the coat proteins of other carlaviruses. The sequence also contains an 11.7K ORF at the 3' terminus, containing a 'zinc-finger' motif which is unique to carlaviruses.Cowpea mild mottle virus (CMMV) has physicochemical properties which resemble those of members of the carlavirus group, namely the presence of filamentous particles c. 650 nm in length, consisting of a coat protein of 31-33K and a single-stranded RNA of Mr 2.5 x 10 6 [Jeyanandarajah and Brunt, 1993]. However, unlike other members of the carlavirus group which are transmitted non-persistently by aphids [Foster, 1992], CMMV is unusual in that it is transmitted in a non-persistent manner by whiteflies (Bemisia tabaci) [Jeyanandarajah and Brunt 1993]. In addition, CMMV has several other unusual properties compared with other carlaviruses, which include, no serological relationships with 18 recognised members of the carlavirus group, and the induction of unusual brush-like intracellular inclusions in infected plants [Brunt et al., 1983]. It has been suggested that CMMV remain unclassified until the taxonomic significance of these differences have been investigated further [Jeyanandarajah and Brunt, 1993].We report here attempts to develop a rapid and specific identification test for carlaviruses which can also be used to determine whether CMMV and similar unclassified viruses are species of the carlavirus genus. The test is based on the polymerase chain reaction (PCR) using primers to conserved and unique sequences in carlavirus RNAs.The overall genome organisation of carlaviruses is very similar to that of potexviruses with the virus genes of both genera being arranged (from 5' to 3') as replicase, a triple gene block (25K, 12K, and 7K), and coat protein open reading frame, with extensive similarity at the amino acid level between the equivalent proteins of potex-and carlaviruses. However, in addition to these proteins, carlavirus genomes contain an additional protein encoded by an open reading frame