Is it new or old growth that is affected? Brown spots could be a micro-nurtient issue. Peppers also need a good amount of light and heat to be successful.

Thanks for your timely reply, NLG1.

It appears to occur on both young and old leaves. As for heat - well, I think there's enough of that. The ambient temperature is in the 20-25 deg C. range. Light? Wouldn't imsufficient light affect the leaf as a whole, causing the whole thing to turn yellow and dry up? The problem observed starts at one or more points between the veins at the edge near the tip of the leaf. The spots increase in size, gradually involve the veins and finally come together until the whole leaf has withered away.