The effect of Cd²⁺ and a combination of Cd²⁺ with non-inhibiting levels of metals like Ca²⁺, Zn²⁺ and Hg²⁺ on the uptake of ammonia and phosphate by Anacystis nidulans IU625 (ATCC 27144) was investigated. Increasing concentrations of Cd²⁺ resulted in the subsequent inhibition of both NH₄⁺ and PO₄^3- uptake. The uptake kinetics was studied by monitoring short-term uptake rates at varying substrate levels. The values for V_max (maximum uptake capacity) and K_m (half saturation constant) were obtained using the double reciprocal plot. The NH₄⁺ uptake as such, was found to be more sensitive to the heavy metal than the PO₄^3- uptake as fairly low levels of Cd²⁺ were sufficient to inhibit the process significantly. However, the uptake kinetics for both NH4+ and PO₄^3- was altered if Cd²⁺ was present in combination with other divalent cations such as Ca²⁺, Zn²⁺ and Hg²⁺. Zn²⁺ acted antagonistically to Cd²⁺ toxicity. Similarly, the Ca²⁺-Cd²⁺ combination protected against inhibition by Cd²⁺ ions. Hg²⁺ behaved differently: the Cd²⁺-Hg²⁺ combination resulted in increased inhibition.