This document describes a protocol for assessing the effect of a nanoparticle formulation on the basic immunologic function of human lymphocytes, i.e. measurement of lymphocyteproliferative responses. This assay will allow for measurement of a nanoparticles’ ability to induce proliferative response of human lymphocytes (part A) or to suppress that induced by phytohemaglutinin (PHA-M) (part B). Parts A and B can typically be run concurrently on the same test plate. Part A is also available as a separate protocol entitled ITA-6.2. Part B is available as a separate protocol with a modification to allow for 24 hr exposure to nanoparticleprior to challenge with PHA-M, and is entitled ITA-6.3.