A pathological nocturnal blood pressure (BP) profile, either non-dipping or reverse dipping, occurs in more than 50% of subjects diagnosed with multiple system atrophy (MSA) or Parkinson's disease (PD). This may play a negative prognostic role in α-synucleinopathies, but, being mostly asymptomatic, remains largely underdiagnosed. In this proof-of-concept study, we aimed at developing a decision-support algorithm to predict pathological nocturnal BP profiles during a standard tilt-table examination in PD and MSA. Sixteen MSA and 16 PD patients underwent standard tilt-table examination and 24-h ambulatory BP monitoring (24-h ABPM). Clinical and tilt test differences between patients with a normal and a pathological nocturnal BP profile at 24-h ABPM were assessed, and a decision-support algorithm was developed accordingly. 75% of MSA and 31 % of PD patients showed a pathological nocturnal BP profile. This was associated with more pronounced orthostatic BP drop (p = 0.03), joint occurrence of orthostatic hypotension and supine hypertension (p = 0.046), and lack of BP overshoot in the late phase II (II_L, p = 0.002) and in the phase IV (p = 0.007) of the Valsalva manoeuvre. Combined ∆BP ≤0.5 mmHg in the II_L and ≤-7 mmHg in the IV phase of Valsalva manoeuvre correctly predicted a pathological nocturnal BP profile with 87.5% sensitivity and 85.7% specificity. Pathological nocturnal BP profiles are associated with evidence of cardiovascular noradrenergic failure in PD and MSA. The Valsalva manoeuvre is routinely performed during standard tilt-table examinations. We propose the naked-eye evaluation of Valsalva phase II_L and phase IV BP behaviour as time-sparing screening tool for pathological nocturnal BP profiles in PD and MSA.