6-phosphofructo-1-kinase (phosphofructokinase; pfk) activity from rhodnius prolixus, a haematophagous insect which is usually a poor flyer, was measured and compared in two metabolically active tissues - flight muscle and fat body. the activity of this important regulatory glycolytic enzyme was much more pronounced in muscle (15.1 ± 1.4 u/mg) than in fat body extracts (3.6±0.4 u/mg), although the latter presented higher levels of enzyme per protein content, as measured by western-blotting. muscle extracts are more responsible than fat body to atp and fructose 6-phosphate, both substrates of pfk. allosteric regulation exerted by different effectors such as adp, amp and fructose 2,6-phosphate presented a singular pattern for each tissue. optimal ph (8.0-8.5) and sensitivity to ph variation was very similar, and citrate was unable to inhibit pfk activity in both extracts. our results suggest the existence of a particular pfk activity for each tissue, with regulatory patterns that are consistent with their physiological roles.