Herb oils of rose-scented geranium cv. Bourbon distilled during summer (May) contained abnormally high concentrations of menthone (38.6%, 47.2%) or 10-epi-γ-eudesmol (22.0%) or citronellol (36.3%) in comparison to the oil produced during winter (citronellol 25.4%, geraniol 23.5%). Significant differences were observed among these oils for other components (linalool, isomenthone, geraniol, citronellyl formate and geranyl formate) also.