Alzheimer’s disease (AD) is a neurodegenerative disease characterised by deposition of β-amyloid (Aβ) and loss of neurones in the cerebral cortex and hippocampus (1). Lysosomal dysfunction and destabilisation have been implicated in a variety of neurodegenerative events, including the apoptotic pathway evoked by Aβ (2). The endocannabinoid system is emerging as a promising neuroprotective target (3), thus the aim of this research was to explore the ability of the endocannabinoid, anandamide (AEA), to maintain lysosomal membrane integrity and confer neuroprotection. Cultured cortical neurones were prepared from one day old Wistar rats. To monitor lysosomal stability, cultured cortical neurones were incubated with acridine orange (AO; 5μg/ml) for 10 minutes followed by treatment with Aβ1-40 (2μM) ± anandamide (AEA; 10nM) for 6 hours. Lysosomal destabilisation was measured by loss of AO fluorescence intensity at 633nm. Release of the lysosomal cathepsin enzymes was measured using a commercially available kit. Expression of the lysosomal associated membrane proteins, LAMP1/2, was assessed by western immunoblotting and apoptosis was measured using the TUNEL procedure. AO fluorescence intensity at 633nm, reflective of intact lysosomes, was significantly reduced from 130±18 (mean fluorescence units ± SEM) in control cells to 52±10 in cells treated with Aβ1-40 (p<0.01, ANOVA, n=5) and this was prevented in cells exposed to Aβ1-40 in the presence of AEA. Cathepsin-L activity was significantly increased from 3.7±0.5 (relative fluorescent units, mean±SEM) to 7.6±1.2 in cells treated with Aβ1-40 (p<0.05, ANOVA, n=5) and this was significantly reduced to 3.5±0.9 in cells exposed to Aβ in the presence of AEA (p<0.05 compared to Aβ treatment, ANOVA, n=5). LAMP1 expression was significantly decreased from 2.70±0.29 (arbitrary units, mean±SEM) to 1.74±0.08 in cells treated with Aβ1-40 compared with control (p<0.05, ANOVA, n=5) and this was prevented by co-treatment with AEA. LAMP2 expression was significantly increased from 3.7±0.15 (arbitrary units, mean±SEM) to 5.9±0.23 by Aβ1-40 (p<0.001, ANOVA, n=5) and this was reduced to 3.9±0.058 in cells treated with Aβ in the presence of AEA. The percentage of TUNEL positive cells was reduced from 24.54±0.96% (mean±SEM) in cells treated with Aβ1-40 to 7.80±0.75% in control cells (p<0.001, ANOVA, n=5). We demonstrate that the endocannabinoid, AEA, prevents the Aβ1-40 -induced lysosomal membrane destabilisation, and the subsequent release of the lysosomal enzyme, cathepsin-L. Similarly, AEA prevents the Aβ1-40-evoked changes in LAMP1 and LAMP2 expression. Modification of the lysosomal branch of the apoptotic cascade by endocannabinoids could be a therapeutic strategy of relevance for AD.