Glucosylceramide transferase (GlcT1) catalyzes the transfer of UDP-glucose to ceramide. The activity of giardial GlcT1 (gGlcT1) is upregulated during encystation. gGlcT1 is a dual substrate enzyme and utilizes both UDP-glucose and UDP-galactose. The rate of galactosylceramide synthesis by gGlcT1 is higher than glucosylceramide. gGlcT1 expression and cyst wall protein synthesis are co-regulated.