The aim of this research was to evaluate the effect of dodecyltrimethylammonium bromide (DTAB) on in vitro permeation of butorphanol through equine nasal mucosa. In vitro permeation studies were done using Franz type diffusion cells and equine mucosa. Two formulations were compared, a control formulation and a formulation containing dodecyltrimethylammonium bromide (DTAB) as penetration enhancer (FI). Flux values at the steady state (J_ss), apparent permeability coefficients (K_p) and lag-time were obtained from the cumulative amount of butorphanol that permeated through equine nasal mucosa and a statistical comparison was performed. The values of J_ss, K_p and lag-time obtained using control formulation and FI did not show statistically significant differences. The addition of DTAB at a concentration of 0.030% W/V is not favourable in the development of intranasal formulations of butorphanol, because it does not improve the passage of butorphanol through equine nasal mucosa.