This paper presents the study results of the embryotoxic effect of the antiviral drug acyclovir in terms of industrial toxicology. Experimental studies were performed on laboratory rats through inhalation modelling of the drug at the concentrations of 0.1 mg/m³ and 1.0 mg/m³. Concentration of 1.0 mg/m³ caused a decrease in placenta size, number of litter and fetal survival with simultaneous increase in crown-rump length.