Endogenous and exogenous opioids modulate reproductive functions in target cells via opioid receptors (µ, δ, and κ). Sperm motility is a metric of gamete functionality, and serves as a suitable parameter for in vitro drug-induced toxicity assays. This study identifies the presence and location of opioid receptors in pig spermatozoa as well as their functional response after in vitro challenge with known agonists (morphine [µ]; [D-Pen 2,5]-enkephanile [δ]; and U 50488 [κ]) and antagonists (naloxone [µ]; naltrindole [δ]; and nor-binaltrorphimine [κ]). Only the µ- and δ-opioid receptors were present in the sperm plasma membrane, overlying the acrosome, neck, and principal piece. Challenge experiments with agonists and antagonists identified both µ- and δ-opioid receptors as regulators of sperm kinematics, wherein µ maintains or increases sperm movement whereas δ decreases sperm motility over time. This article is protected by copyright. All rights reserved.