['To determine whether elevated microviscosity is associated with elevated arterial pressure in segregating (F2) hybrids produced by crossing stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats.', 'SHRSP and WKY rats were obtained from the colony at the University of Heidelberg. F2 progeny were obtained by brother-sister mating of the F1 progeny of the cross between SHRSP and WKY rats. Membrane microviscosity (the inverse of fluidity) was measured as a fluorescence anisotropy of trimethylammonium diphenylhexatriene incubated with the erythrocyte membranes. The measurements were made using a luminescence spectrometer with computer-controlled excitation and emission polarizers.', 'Membrane microviscosity was significantly greater (fluidity was lower) in erythrocyte membranes obtained from SHRSP than in those obtained from WKY rats. In the F2 cohort there were no significant correlations between membrane microviscosity and systolic blood pressure, diastolic blood pressure, salt-loaded systolic blood pressure or salt-loaded diastolic blood pressure. A similar lack of relationship between these parameters was shown in a subgroup analysis, in which males or females with a male WKY rat progenitor and males or females with a male SHRSP progenitor were analysed separately.'] Does membrane microviscosity correlate with blood pressure : a cosegregation study?