The present invention provides apparatus and methods for injection moulding polymeric cannulae from liquid polymeric materials. The method includes injecting pressurised liquid polymer into a mould cavity and into an overflow and forming a conduit by forcing pressurised working fluid through the solidifying liquid polymer into the overflow. The invention provides a mould for fluid-assisted injection moulding articles from polymeric materials, the mould comprising at least two parts defining a cavity having a conduit portion incorporating a needle portion; a channel for liquid polymer ingress; a channel for pressurised fluid ingress; and an overflow in communication with the conduit portion. The mould may incorporate a plurality of cavities. Preferably the volume of the overflow is equal to or greater than the volume of the conduit portion. Preferably the mould incorporates a separating means for separating the overflow from a cannula portion of an article formed in the mould.