On September 20, 2023, the Organization for Economic Cooperation and Development (OECD) will hold a webinar on Test Guideline No. 126: Determination of the Hydrophobicity Index of Nanomaterials Through an Affinity Measurement. The webinar will present the method to determine the hydrophobicity index (Hy) of nanomaterials, through an affinity measurement, described in the OECD Test Guideline (TG) No. 126. According to OECD, webinar attendees will be able to learn the use and limitation of the TG, as well as about the validation exercise that was done to support its development. OECD will provide simultaneous interpretation in English and Spanish. Registration is open.