To determine whether intracellular calcium could be involved in regulating gelatinase production, bovine synovial fibroblasts were incubated with the calcium ionophores A23187 or ionomycin. Addition of calcium ionophore stimulated production of a gelatinase with an apparent molecular weight of 144 kDa. To ensure that the calcium ionophore was elevating cytosolic free calcium levels, calcium levels were determined using Indo-1. Addition of 0.1 microM ionomycin raised [Ca2+]i up to 1053 +/- 163 nM (mean +/- SD). Our data shows that calcium ionophore A23187 stimulates production of a high molecular weight gelatinase. The appearance of p144 gelatinase correlates with an increase in intracellular calcium.