Acetyl-L-carnitine (LAC) is a neuroactive compound that is thought to be involved in cholinergic transmission. The effects of acute intravenous LAC administration (30 mg/kg) on pattern-evoked electroretinograms (P-ERGs) were evaluated in nine healthy volunteers ranging in age between 21 and 27 years. Nine age-matched, normal subjects treated with a placebo served as controls. Steady-state (8 Hz) P-ERGs recorded in response to counterphased sinusoidal gratings of variable spatial frequency (0.6-4.8 cycles/degree) were obtained before and at 20, 50 and 80 min after LAC or placebo administration. The amplitude and phase of the Fourier-analysed P-ERG second harmonic were measured. As compared with placebo-treated controls, LAC-treated subjects showed a selective P-ERG amplitude increase (Mann-Whitney rank test: P less than 0.05), which was found 80 min posttreatment at a spatial frequency of 4.8 cycles/degree. For the same stimulus a significant (P less than 0.05) P-ERG phase shortening (at 50 min after drug administration) was also found. The spatial frequencies of other stimuli did not show a significant difference between the LAC- and placebo-treated groups. These results indicate that acute LAC administration induces a spatial-frequency-dependent enhancement of the human P-ERG. This is compatible with a cholinergic excitatory effect and suggests a therapeutic role for this compound in retinal dysfunctions with selective vulnerability to medium-high spatial frequencies.