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 beta1-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 (beta = 0.096, P < 0.001), systolic BP (beta = 0.09, P = 0.021) and diastolic BP (beta = 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 Gly389 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 beta1-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.