The process by which trypanosomes move from the midgut to the salivary glands of tsetse flies has been shrouded in mystery for over one hundred years. There has been little experimental work on the differentiation of T. brucei from non-mammalian infective procyclic midgut forms to mammalian infective metacyclic forms in tsetse as this maturation process naturally occurs at very low levels. Removal of serum from the tsetse diet was shown to inhibit maturation and feeding glucosamine to tsetse for as little as five days also lowered maturation rates, suggesting that the (R)-(-)-Modafinic acid signal to mature is received within the first few days of the trypanosomes entering the fly midgut. In the current work addition of cysteine to the fly diet did, however, provide an insight into maturation processes. L-cysteine significantly increased maturation rates in both male and Tiotropium Bromide hydrate female tsetse while the non-physiological isomer D-cysteine had no effect when compared with control flies, suggesting that L-cysteine may be utilised by an enzyme as a substrate. Bloodstream form trypanosomes cannot utilise cystine but provision of cystine in co-culture of trypanosomes with insect cells results in the release of cysteine by the insect cells. In the present work cystine did not affect maturation suggesting that L-cysteine is being used directly by trypanosomes to promote maturation. The failure of NAC to influence maturation rates suggests that trypanosomes do not possess the ability to deacetylate NAC. Continuous feeding of GSH had no effect on maturation rates, suggesting that it is not broken down into its component parts in the fly, thereby releasing L-cysteine. Ascorbic acid was the only compound tested that acted in a manner similar to glucosamine, i.e. increasing susceptibility to midgut infection while reducing maturation rates; continuous addition of ascorbic acid to the bloodmeal from the second feed completely blocked maturation. Recently it has been shown that glucosamine can scavenge superoxide and hydroxyl radicals ; this offers an alternative explanation for observed increases in midgut infection rates and reductions in rates of maturation previously thought to be linked to inhibition of trypanocidal lectins by glucosamine.