AbstractThe sublethal biochemical effects of pentachlorophenol (PCP) were investigated in live, intact red abalones (Haliotis rufescens), using a flow‐through exposure system, by in vivo31P NMR spectroscopy. Based on rangefinding tests (6‐hr LC50= 1.6 mg/L; 6‐hr no‐observable‐effect‐level (NOEL) = 0.8 mg/L), three abalones were separately exposed to a sublethal concentration (1.2 mg/L) for 5 hr, followed by a 13 hr recovery period. Effects in foot muscle included both a decrease in phosphoarginine and an increase in inorganic monophosphate concentrations ([PA] and [Pi], respectively); both foot muscle concentrations of adenosine triphosphate [ATP]and intracellular pH (pHi) also declined. Parallel in vitro experiments revealed that concentrations of glycerol 3‐phosphate, lactate, citrate, succinate, malate, and alanine (Ala) all increased, while those of glyceraldehyde 3‐phosphate and glutamine (Gln) remained stable. Also, these effects were not evident until 2 hr into exposure, possibly the time required for PCP to attain an effective concentration in foot muscle. During recovery, while Pideclined to pre‐exposure levels, [PA] completely recovered in only one individual. Also, realkalinization of pHiwas similar to recovery of [Pi], and ATP returned to near‐initial levels, as did glycerol 3‐phosphate, lactate, succinate, malate, and Ala; glyceraldehyde 3‐phosphate, citrate, and Gln levels declined. Recovery responses corresponded to the time for PCP clearance from foot muscle. The effects of PCP were similar to those of hypoxia, fatigue, hypersalinity, and arginine kinase inhibitors, and so sublethal PCP concentrations may also inhibit electron transport and arginine kinase as well as uncouple mitochondrial oxidative phosphorylation in intact molluscs. Thus, the effects of pollutants on key biochemical processes may now be measured in intact aquatic organisms as they occur, improving our ability to accurately assess the environmental effects of pollu