Limb activity meters, otherwise modified self-winding watches that can record limb agitative movements such as in itch-provoked scratch, were introduced for an objective evaluation of the relative effectiveness of three antipruritic drugs: chlorpheniramine, cyproheptadine, and sulphapyridine for palliating pruritus associated with chloroquine chemosuppressive treatment of acute malarial febrile paroxysms in eighteen adult patients. Six fit and healthy subjects were also studied to obtain data for unmedicated controls. The meters were used to monitor the upper and lower limb activities of the patients during nocturnal sleep for 6 hours over 3 consecutive nights, after they had developed the chloroquine-induced pruritus and were then administered the antipruritic medications, six patients per drug, by a random selection. Sulphapyridine antipruritic treatment significantly reduced the activities of the upper limbs of itchy patients much greater than did cyproheptadine (P < 0.0001, right hand; P < 0.01 left hand). However sulphapyridine-treated patients still itched significantly more than controls from the greater activities in the dominant right hand of the patients (P < 0.05). Cyproheptadine had a marginally-better performance than chlorpheniramine, generally, in palliating the chloroquine-induced pruritus but only in one of 3 nights, for the right hand recordings, were the limb activities significantly different. There was no significant difference observed in the activities of the lower limbs for the unmedicated controls compared to itchy patients, irrespective of the antipruritic treatment mode. Five out of the 6 patients treated with sulphapyridine also complained of anorexia plus a feeling of fullness or indigestion.(ABSTRACT TRUNCATED AT 250 WORDS)