The capacity for autonomous replication of the DNA A of African cassava mosaic virus (ACMV), a member of the bipartite geminiviruses infecting dicotyledonous plants, has been compared in host and non-host cells. A derivative of the ACMV DNA A was transfected into tobacco and maize protoplasts. Although ACMV is not able to infect maize, replication of the DNA A in maize protoplasts was observed to occur. The efficiency of replication was 10 to 20% of that seen in tobacco protoplasts. In both plant systems, replication was detected after the onset of cell division. ACMV replication in maize cells was compared to that of wheat dwarf virus and found to be 10 to 20% of that observed with the monocotyledon-specific virus. Insertion of 1165 bp of non-viral DNA into the ACMV DNA A prevented replication in maize but not in tobacco.