Although the number of vaccines and diagnostic tests currently delivered intradermally is limited, this route of administration offers potential advantages due to the high concentration of antigen-presenting cells in the skin. One factor which may in part be limiting development and use of intradermal (ID) administration is concern about the ease and reliability of the needle and syringe-based Mantoux technique. A phase I clinical study was conducted to evaluate two ID adapters that have been developed as injection-delivery aids to increase the safety, simplicity, and reliability of ID injection: a prototype autodisable, intradermal (ADID) adapter for autodisable (AD) syringes, and a marketed side-merge adapter (SMA). Thirty healthy adult volunteers each received six injections of 0.1 mL of sterile saline solution. Each adapter was used to give injections into the upper deltoid, forearm, and suprascapular regions of each volunteer. The needle-bevel orientation during injection was random. Injection performance was determined by measuring wheal size and fluid leakage. Wheals were similar in size for the ADID adapter (mean 9.9 ± 0.17 mm) and SMA (mean 9.8 ± 0.15 mm). In all of the injections completed with the SMA, and 98% of those completed with the ADID, fluid leakage was less than 10% of the intended injection volume. Minor skin abrasions were the only adverse events. Based on self-reporting of pain, injections were well tolerated (mean pain score of 2 on a 0–10 scale). ID delivery using the SMA and ADID adapters appears safe and effective.