In a heterogeneous environment of virtual machines, an agent can migrate between virtual machines of different virtual machine types. During migration, objects of the serialized stream, e.g. representing a mobile agent, may need to be instantiated on the new virtual machine. Where the resources required to instantiate an object are missing on the virtual machine, the virtual machine may use connection information recorded when the serialized stream was received to connect to the source machine and request the required resources (e.g. the type for the object) from the source machine. A resource request to the source machine may specify a virtual machine type of the requesting virtual machine, thereby enabling the source machine to retrieve the correct instance of the type to return to the virtual machine.