Plasma levels of progesterone, prolactin, luteinizing hormone, and electrolytes were monitored by radioimmunoassay in ten cycling buffaloes maintained at Punjab Agricultural University, Ludhiana during the hot summer months of June-July. The plasma progesterone concentration ranged from 0.28 +/- 0.04 to 3.09 +/- 0.03 ng/ml at various stages of the oestrous cycle. Prolactin values ranged from 319 +/- 23 to 371 +/- 25 ng/ml and LH levels from 0.95 +/- 0.05 to 1.35 +/- 0.08 ng/ml. Concentrations differed significantly (P less than or equal to 0.05) at various stages of the cycle. Levels of electrolytes, viz. Ca++, Na+ and K+, were well within the normal range. The high levels of prolactin, progesterone and LH during the hot summer were assessed in relation to poor reproductive efficiency in buffaloes.