Abstract: A needle holder assembly having a sleeve that slidably receives a needle holder having a needle assembly attached thereto. After the need holder assembly has been used to collect a sample of body fluid, the needle holder is slid from its initial retracted position to a permanently locked extended position. In the extended position the used needle is contained within the sleeve of the assembly and can be disposed of. The assembly of the present invention includes a mechanism for smoothly releasing the needle holder from the retracted position, an improved mechanism for permanently and securely locking the needle holder in the extended position, and a body fluid collection channel around the distal end of the sleeve that prevents body fluid from splattering from the distal end of the assembly, when the sleeve is locked in the needle holder.