Investigations were undertaken to observe the influence of technical grade carbofuran (CF) on the egg maturational processes of catfish, Heteropneustes fossilis (Bloch). Fish were exposed to sublethal doses (0.5, 1, and 2 mg/L) of CF for 30 days at 25 +/- 1 degrees C. Control fish were maintained in water. The gonado-somatic index (G.S. I. = ovarian weight x 100/body weight) of the fish, treated with 1 or 2 mg/L CF, was decreased significantly compared to that of the controls. The inhibition was almost at the same level in these doses. CF at the dose of 0.5 mg/L was found to be ineffective. From the histomorphological observations of the ovary, it was observed that CF altered both the area and the percentage occurrence of the various types of primary oocytes in the ovary compared to that of the control fish. The stage I primary oocytes were predominantly higher in CF-treated fish than stage II and stage III which was reversed in control animals. The degeneration of follicular walls, connective tissues and vacuolization in the ooplasm of the stage II and III oocytes were observed in CF-treated fish (0.5-2 mg/L). It appears that CF at sublethal concentrations inhibits oocyte maturational processes in catfish.