Sequential delivery syringes including a valve mechanism are configured and configurable to enable one or more substances to be prefilled into the syringe. The valve mechanism may be an aspect of a distal seal assembly. Actuation of the valve mechanism permits opening of a fluid passage for the mixing of one or more substances, and the resulting mixed substance can be delivered by the syringe, for example, for administration of a pharmaceutical to a subject. The sequential delivery of substances contained in a distal and proximal chamber is also provided, where a second substance from the distal chamber is delivered followed by the delivery of a first substance from the distal chamber after the first substance from the proximal chamber is transferred into the distal chamber involving the actuation of the valve mechanism.