We have investigated the effects of electric field pulses (of about 44 kV/cm magnitude and 30 [mu]sec duration) on E. coli ribosomal RNA in solution (5 x 10-4 M sodium cacodylate buffer, pH 7, 20° C). The time course of changes in ultraviolet absorbance and electric dichroism can be resolved into contributions from orientational and conformational changes. The fast part of the relaxation spectrum (completed in less than 1 [mu]s) is attributed to alignment of double-helical segments of rRNA with the external electric field; the slower part (relaxation times in the ms and [mu]s range) is shown to be due to changes in orientation of the entire rRNA molecule, concomitant with electric field-induced helix-coil transitions of oligomeric base-paired regions.