OSA (obstructive sleep apnoea) stimulates sympathetic nervous activity and elevates resting HR (heart rate) and BP (blood pressure). In the present study in a cohort of 309 untreated OSA patients, the resting HR and BP during the daytime were correlated with AHI (apnoea/hypopnea index) and compared with patients with R389R ( n =162), R389G ( n =125) and G389G ( n =22) genotypes of the β 1 -adrenoreceptor R389G polymorphism. We analysed the impact of the genotype on the decline of HR and BP in a subgroup of 148 patients (R389R, n =86; R389G, n =54; G389G, n =8) during a 6-month follow-up period under CPAP (continuous positive airway pressure) therapy during which cardiovascular medication remained unchanged. In untreated OSA patients, we found an independent relationship between AHI and resting HR (β=0.096, P <0.001), systolic BP (β=0.09, P =0.021) and diastolic BP (β=0.059, P =0.016). The resting HR/BP, however, did not differ among carriers with the R389R, R389G and G389G genotypes. CPAP therapy significantly reduced HR [−2.5 (−1.1 to −4.0) beats/min; values are mean difference (95% confidence intervals)] and diastolic BP [−3.2 (−1.5 to −5.0) mmHg]. The decline in HR was more significantly pronounced in the R389R group compared with the Gly 389 carriers [−4.1 (−2.3 to −5.9) beats/min ( P <0.001) compared with −0.2 (2.1 to −2.6) beats/min ( P =0.854) respectively; Student's t test between groups, P =0.008]. Diastolic BP was decreased significantly ( P <0.001) only in Gly 389 carriers (R389G or G389G) compared with R389R carriers [−5.0 (−2.3 to −7.6) mmHg compared with −2.0 (0.4 to −4.3) mmHg respectively]. ANOVA revealed a significant difference ( P =0.023) in HR reduction between the three genotypes [−4.1 (±8.4) beats/min for R389R, −0.5 (±9.3) beats/min for R389G and +1.9 (±7.2) beats/min for G389G]. In conclusion, although the R389G polymorphism of the β 1 -adrenoceptor gene did not influence resting HR or BP in untreated OSA patients, it may modify the beneficial effects of CPAP therapy on these parameters.