Abstract. The resonance transition (n, l) = (40, 36) → (41, 35) of the antiprotonic helium (p 4 He + ) isotope at a wavelength of 1154.9 nm was detected by laser spectroscopy. The population of p 4 He + occupying the resonance parent state (40, 36) was found to decay at a rate of 0.45 ± 0.04 µs −1 , which agreed with the theoretical radiative rate of this state. This implied that very few long-lived p 4 He + are formed in the higher-lying states with principal quantum number n ≥ 41, in agreement with the results of previous experiments.