Oral beta-alanine (beta A) doses larger than 800 mg commonly result in unpleasant sensory symptoms (paresthesia). However, the association of form (pure vs. slow-release) with side-effects has not been fully described. The aim of this single-blinded, randomized three-arm clinical trial was to compare plasma kinetics and symptoms following beta A bolus administration in solution or in slow-release tablet form. Eleven healthy adults ingested 1.6 g of a pure beta A reference solution (REF), 1.6 g in slow-release beta A tablets (TAB) or a placebo (PLA) after an overnight fast. During the next 6 h, urinary and plasma beta A concentrations were measured and questionnaires about intensity, nature (pins and needles, itching, flushing, irritation, numbness, soreness), and spatial distribution of unusual sensations were filled in. TAB resulted in a smaller peak plasma concentration than REF (82 vs. 248 mu mol L-1, p < 0.001), delayed time to peak (1.0 vs. 0.5 h, p < 0.01) no difference in area under the curve, reduced loss in urine (202 vs. 663 mu mol, p < 0.0001), and improved retention (98.9 vs. 96.3%, p < 0.001). Symptoms described as "pins and needles" were perceived rapidly on the skin of the arms and trunk after REF (T (max) = 15 min) and their time course nearly mimicked plasma concentrations. Maximum intensity scores were weaker with TAB ("very low") than with REF ("low", p < 0.001), while TAB and PLA did not differ with respect to side-effects. In summary, ingesting 1.6 g beta A in slow-release tablets rather than pure in solution results in slower absorption kinetics, improved whole body retention and sensory side-effects that cannot be differentiated from PLA.